Turn frontend Tripperware into a Middleware.

[jeschkies]

What this PR does / why we need it:
Currently, a request to Loki's frontend API goes through these conversions:

        http.Request 
            ↓ limitedRoundTripper
        queryrangebase.Request
            ↓ queryrangebase.Middlware
        … 
            ↓
        queryrangebase.Request
            ↓ limitedRoundTripper  
        http.Request
            ↓ grpcRoundTripperAdapter
        httpgrpc
            ↓ grpcRoundTripperAdapter
        http.Response
            ↓ limitedRoundTripper
        queryrangebase.Response
            ↓ limitedRoundtripper
        http.Response

Since httgrpc and queryrangebase.Request are Protobufs there's no good reason to encode and decode them to HTTP responses/requests. Furthermore, the encoding to HTTP makes it harder for us to encode query plans.

Thus the conversions are changed to the following:

        http.Request 
            ↓
        queryrangebase.Request
            ↓ queryrangebase.Middlware
        … 
            ↓
        queryrangebase.Request
            ↓
        httpgrpc
            ↓
        queryrangebase.Response
            ↓
        http.Response

In order to achieve this the http.RoundTripper is pushed to the outside. Only the serialization layer from http.Request to queryrangebase.Request and http.Response to queryrangebase.Response will be an http.RoundTripper. Everything else is either a queryrangebase.Handler or queryrangebase.Middleware.

This change has been split up

• Replace LokiLabelNamesRequest with logproto.LabelRequest. #10801
• Support protobuf QueryRequest in querier. #10858
• Define QueryResponse and QueryRequest protobufs. #10956.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
  • If the change is worth mentioning in the release notes, add add-to-release-notes label
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR