otelgrpc: Deprecate the interceptors

[pellared]

I think we should also update the existing examples to use the new instrumentation.

I propose to:

1. Merge this PR
2. Create an issue for https://github.com/open-telemetry/opentelemetry-go-contrib/pull/3002/files#r1209293763
3. Update the existing examples to use the new functionality.
4. Deprecate the interceptors so that they are available in next release.
5. After the next release remove the interceptors.

@open-telemetry/go-approvers please upvote/downvote if you agree or not. Feel free to leave any additional feedback.

Originally posted by @pellared in #3002 (review)

1. Blocked by otelgrpc: Add metrics support for stats handler #4316
2. Deprecate the interceptors
3. Update the docs so that grpc.StatsHandler is the first-class citizen

[pellared]

FYI @fatsheep9146