Add nil check for billing mode in AWS DynamoDB events driver

[xacrimon]

Turns out, AWS is inconsistent in what fields they set and they don't always set the BillingModeSummary field if the table is in provisioned mode. Wasn't able to find that noted anywhere so I assumed it would be, this turned out to be incorrect.

This PR adds some pessimistic null-checks and assumed the billing mode is provisioned if the fields are not set. Still not sure when they are set, just that they sometimes aren't. This was further not helped by our AWS tests somehow not failing on a panic, they just seem to pause and continue? That's for another PR though.

This also fixes a panic case in dynamic.go if the provided map is lacking an event type key which caused AWS tests to fail.

Fix #12443

[Tener]

It would be good to have some tests along with these changes.

[Tener]

From failed unit tests:

panic: reflect: call of reflect.Value.IsNil on string Value

goroutine 11921 [running]:
reflect.Value.IsNil(...)
	/opt/go/src/reflect/value.go:1440
github.com/gravitational/teleport/lib/events.isInterfaceNil({0x4449fa0, 0xc00422f4b0})
	/workspace/lib/events/dynamic.go:33 +0x25f
github.com/gravitational/teleport/lib/events.FromEventFields(0x5a1fff8)
	/workspace/lib/events/dynamic.go:50 +0xc5
github.com/gravitational/teleport/lib/events.(*FileLog).searchEventsWithFilter(0xc008fc4658, {0xcb17b4, 0x0, 0x0}, {0xc008fc4df8, 0x0, 0x0}, {0x0, 0x75b18c0}, 0x1f4, ...)
	/workspace/lib/events/filelog.go:229 +0x57a
github.com/gravitational/teleport/lib/events.(*FileLog).SearchEvents(0xc0036ea120, {0xc008fc4a88, 0x0, 0x0}, {0x59e25a0, 0xc0076ce480, 0x0}, {0xc00962f049, 0x7}, {0xc005745340, ...}, ...)
	/workspace/lib/events/filelog.go:171 +0x347
github.com/gravitational/teleport/lib/events.(*AuditLog).SearchEvents(0xc001760000, {0x5a584b0, 0xc008ce0360, 0x0}, {0x5a9ee88, 0x4668da0, 0x0}, {0xc00962f049, 0x7}, {0xc005745340, ...}, ...)
	/workspace/lib/events/auditlog.go:874 +0x5eb
github.com/gravitational/teleport/lib/auth.(*ServerWithRoles).SearchEvents(0xc006fc4310, {0x48e6244, 0x2, 0x0}, {0xc001287050, 0x29, 0x0}, {0xc00962f049, 0x7}, {0xc005745340, ...}, ...)
	/workspace/lib/auth/auth_with_roles.go:3760 +0x1b8
github.com/gravitational/teleport/lib/auth.(*GRPCServer).GetEvents(0x0, {0x5a584b0, 0xc008ce0390}, 0xc004bdab40)
	/workspace/lib/auth/grpcserver.go:2867 +0x26c
github.com/gravitational/teleport/api/client/proto._AuthService_GetEvents_Handler.func1({0x5a584b0, 0xc008ce0390}, {0x482b000, 0xc004bdab40})
	/workspace/api/client/proto/authservice.pb.go:16443 +0x8c
github.com/gravitational/teleport/lib/auth.(*Middleware).withAuthenticatedUserUnaryInterceptor(0x5a30e5, {0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40}, 0x9, 0xc009016ca8)
	/workspace/lib/auth/middleware.go:394 +0xc6
github.com/gravitational/teleport/lib/utils.ChainUnaryServerInterceptors.func1.1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40})
	/workspace/lib/utils/grpc.go:48 +0x8f
github.com/gravitational/teleport/lib/limiter.(*Limiter).UnaryServerInterceptorWithCustomRate.func1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40}, 0xc006a67aa0, 0xc006a67b40)
	/workspace/lib/limiter/limiter.go:149 +0x2da
github.com/gravitational/teleport/lib/utils.ChainUnaryServerInterceptors.func1.1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40})
	/workspace/lib/utils/grpc.go:48 +0x8f
github.com/gravitational/teleport/lib/utils.ErrorConvertUnaryInterceptor({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40}, 0x3, 0xc006a67ba0)
	/workspace/lib/utils/grpc.go:27 +0x5c
github.com/gravitational/teleport/lib/utils.ChainUnaryServerInterceptors.func1.1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40})
	/workspace/lib/utils/grpc.go:48 +0x8f
github.com/grpc-ecosystem/go-grpc-middleware/v2/interceptors.UnaryServerInterceptor.func1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40}, 0xc006a67aa0, 0xc006a67bc0)
	/go/pkg/mod/github.com/grpc-ecosystem/go-grpc-middleware/[email protected]/interceptors/server.go:22 +0x2e4
github.com/gravitational/teleport/lib/utils.ChainUnaryServerInterceptors.func1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40}, 0xc006a67aa0, 0xc009016ca8)
	/workspace/lib/utils/grpc.go:52 +0x21f
google.golang.org/grpc.chainUnaryInterceptors.func1.1({0x5a584b0, 0xc008ce00c0}, {0x482b000, 0xc004bdab40})
	/go/pkg/mod/google.golang.org/[email protected]/server.go:1116 +0x126
go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc.UnaryServerInterceptor.func1({0x5a584b0, 0xc002508360}, {0x482b000, 0xc004bdab40}, 0xc006a67aa0, 0xc0041a43c0)
	/go/pkg/mod/go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/[email protected]/interceptor.go:325 +0x797
google.golang.org/grpc.chainUnaryInterceptors.func1.1({0x5a584b0, 0xc002508360}, {0x482b000, 0xc004bdab40})
	/go/pkg/mod/google.golang.org/[email protected]/server.go:1119 +0x227
google.golang.org/grpc.chainUnaryInterceptors.func1({0x5a584b0, 0xc002508360}, {0x482b000, 0xc004bdab40}, 0xc006a67aa0, 0xc009016ca8)
	/go/pkg/mod/google.golang.org/[email protected]/server.go:1121 +0x286
github.com/gravitational/teleport/api/client/proto._AuthService_GetEvents_Handler({0x48d81c0, 0xc00411fcb0}, {0x5a584b0, 0xc002508360}, 0xc008cca8a0, 0xc006e47820)
	/workspace/api/client/proto/authservice.pb.go:16445 +0x1db
google.golang.org/grpc.(*Server).processUnaryRPC(0xc001bc7880, {0x5a9fca0, 0xc0054d96c0}, 0xc002b51e60, 0xc003479cb0, 0x75c9588, 0x0)
	/go/pkg/mod/google.golang.org/[email protected]/server.go:1282 +0x1532
google.golang.org/grpc.(*Server).handleStream(0xc001bc7880, {0x5a9fca0, 0xc0054d96c0}, 0xc002b51e60, 0x0)
	/go/pkg/mod/google.golang.org/[email protected]/server.go:1619 +0xfd4
google.golang.org/grpc.(*Server).serveStreams.func1.2()
	/go/pkg/mod/google.golang.org/[email protected]/server.go:921 +0xfe
created by google.golang.org/grpc.(*Server).serveStreams.func1
	/go/pkg/mod/google.golang.org/[email protected]/server.go:919 +0x4d1
FAIL	github.com/gravitational/teleport/lib/web	130.579s

[xacrimon]

@Tener I'd love to have reliable tests where I can query against AWS or use an emulator to test this. The issue is that AWS is at best inconsistent here and I've observed multiple variations of populated fields in cases that aren't really distinct which worries me. Same goes for the AWS emulator, which populates them all regardless as one would expect.

[xacrimon]

I'll add some test checks for the dynamic.go changes though. I could potentially construct some nil-check tests for AWS but they seem of dubious value to me since I hardly know what behaviour to expect from AWS.

[zmb3]

Please try running this against a real dynamo instance in both billing modes before merging.

[xacrimon]

Please try running this against a real dynamo instance in both billing modes before merging.

@zmb3 Yep, done. Did that previously as well for the first PR. Issue was that AWS API is inconsistent in what fields it populates and contains zero docs on when it decides to populate certain fields.

[github-actions]

@xacrimon See the table below for backport results.

Branch	Result
branch/v9	Failed