gcp/observability: implement logging via binarylog

[lidizheng]

The plugin registers a binarylog Logger and consumes a binarylog Sink directly from the internal API, without any temporary file in between.

The designed usage looks like:

import "google.golang.org/grpc/observability"

func main() {
    if err := observability.Start(context.Background()); err != nil {
        // Handle the error
    }
    defer observability.End()
    // Use gRPC as normal
}

There is still vagueness inside the proto definition (grpc/grpc-proto#103, pending to be formed as gRFC). As discussed before, I hid them as internal module. The translation between binary log entry and GrpcLogRecord is almost 1-to-1, but misses details like:

• Service name and method name won't present in all events
• Peer address is not available in client initiated request
• New proto doesn't have payload length

Previous attempt: #5157

RELEASE NOTES: none

[lidizheng]

@dfawley PTAL.

[lidizheng]

Thanks for the quick review!

I addressed all comments (or at least try to come up with a solution).

PTALA.

[lidizheng]

@dfawley How's the review going? Feel free to post partial or high-level comments. Let me know how can I push this PR forward.

[lidizheng]

@dfawley PTALA. I have updated this PR according to our offline discussion. The data race around binarylog logger is resolved.

[lidizheng]

Thanks for the quick review! PTALAAA.

[lidizheng]

@dfawley PTALAAAA. I have lined up 2 child PRs after this #5233, #5234.

[lidizheng]

Bump.