receive: Allow specifying a custom gRPC service config via flag

[philipgough]

receive: Adds a flag to allow specifying custom behaviour for gRPC.

The flag needs to be a JSON string as defined by https://github.com/grpc/grpc/blob/d0a7c33b43d14adafcec9379d40ae09c7ba76bf9/doc/service_config.md

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

Verification

[MichaHoffmann]

Why only for receiver though? Wouldn't all grpc APIs make sense?

[philipgough]

Why only for receiver though? Wouldn't all grpc APIs make sense?

Potentially. Probably less of in a need in other components to tweak this but I am happy to add it if there is a perceived benefit. I was trying to tackle the problem discussed here for receive.

I see for example query is using a hardcoded config for endpoint groups

thanos/pkg/extgrpc/client.go

Line 27 in dc4c49f

func EndpointGroupGRPCOpts() []grpc.DialOption {

[saswatamcode]

Seems good to me!
I'd also want the same flag in other components, as it seems useful to tune @philipgough

[philipgough]

I'd also want the same flag in other components, as it seems useful to tune

@saswatamcode ack, do you want them added to this PR?

[saswatamcode]

Let's do in future PRs