ccl/sqlproxyccl: add helpers related to connection migration

Informs cockroachdb#76000. Extracted from cockroachdb#76805.

This commit adds helpers related to connection migration. This includes support
for retrieving the transfer state through SHOW TRANSFER STATE, as well as
deserializing the session through crdb_internal.deserialize_session.

We also introduce a new error marker for errors that denote connections which
are recoverable. In our case, we convert SQL errors from first column of the
SHOW TRANSFER STATE query (e.g. serialization errors) to Go errors, and mark
them with the errConnRecoverableSentinel sentinel.

Release note: None

pkg/ccl/sqlproxyccl/BUILD.bazel

@@ -6,6 +6,7 @@ go_library(
     srcs = [
         "authentication.go",
         "backend_dialer.go",
+        "conn_migration.go",
         "connector.go",
         "error.go",
         "forwarder.go",
@@ -28,7 +29,9 @@ go_library(
         "//pkg/security/certmgr",
         "//pkg/sql/pgwire",
         "//pkg/sql/pgwire/pgcode",
+        "//pkg/sql/pgwire/pgwirebase",
         "//pkg/util/contextutil",
+        "//pkg/util/encoding",
         "//pkg/util/grpcutil",
         "//pkg/util/httputil",
         "//pkg/util/log",
@@ -52,6 +55,7 @@ go_test(
     size = "small",
     srcs = [
         "authentication_test.go",
+        "conn_migration_test.go",
         "connector_test.go",
         "forwarder_test.go",
         "frontend_admitter_test.go",
@@ -65,6 +69,7 @@ go_test(
         "//pkg/base",
         "//pkg/ccl/kvccl/kvtenantccl",
         "//pkg/ccl/sqlproxyccl/denylist",
+        "//pkg/ccl/sqlproxyccl/interceptor",
         "//pkg/ccl/sqlproxyccl/tenantdirsvr",
         "//pkg/ccl/sqlproxyccl/throttler",
         "//pkg/ccl/utilccl",
@@ -75,6 +80,7 @@ go_test(
         "//pkg/sql",
         "//pkg/sql/pgwire",
         "//pkg/sql/pgwire/pgerror",
+        "//pkg/sql/pgwire/pgwirebase",
         "//pkg/testutils",
         "//pkg/testutils/serverutils",
         "//pkg/testutils/skip",