Encode gRPC logs with zap and emit to stdout

[vprithvi]

Requirement - what kind of business use case are you trying to solve?

It appears that gRPC logs are not json formatted, which implies that they are not using zap

Proposal - what do you suggest to solve the problem or improve the existing situation?

Use zap and emit grpc logs to stdout

[yurishkuro]

grpc uses its own logging API, that needs to be wrapped to work with zap.

we can probably use this: https://github.com/grpc-ecosystem/go-grpc-middleware/blob/master/logging/zap/doc.go

[yurishkuro]

There's a PR #1330 trying to address this, but it needs rebasing.