Feature: Add FTV1 Support via Handler

[lleadbet]

This adds the ability to properly respond to Apollo Federation v1 (aka ftv1) headers with traces to support field-level traces within Apollo Studio. This feature is entirely optional, and would be opted in as with the existing Apollo Tracing handler.

Sample: https://github.com/lleadbet/apollo-gqlgen-ftv1/blob/master/server.go#L24

To support this, there are two major changes:

• Added dependency on Protobuf, as Apollo uses it for marshaling the format
• Updates the RawParams to support passing request headers to Handlers

Beyond that, it adds the plugin itself alongside the source of the protobuff file to be able to use as reference.

Not sure where docs should be updated, however.

I have:

• Added tests covering the bug / feature (see testing)
• [] Updated any relevant documentation (see docs)

[coveralls]

Coverage decreased (-0.06%) to 74.671% when pulling 1a5dcfd on lleadbet:master into 0465dcb on 99designs:master.

[lleadbet]

Also- if there's a good way to note to coveralls that the protobuf/generated files can be exempt, that'd be ideal since the length of both files is tanking overall coverage.

[StevenACoffman]

Thanks!

[StevenACoffman]

See #2133

[StevenACoffman]

Also, looks like you need to run:

go mod download google.golang.org/protobuf

[lleadbet]

As a followup, this also marks all of Apollo's tests as passing using their test suite:

Language	Library	Federation 1 Support	Federation 2 Support
Go	gqlgen	_service ✅ @key (single) ✅ @key (multi) ✅ @key (composite) ✅ @requires ✅ @provides ✅ @ftv1 ✅	@link ✅ @Shareable ✅ @tag ✅ @OverRide ✅ @inaccessible ✅

[lleadbet]

Same as last time: apollographql/apollo-federation-subgraph-compatibility#89

Will get that pushed through to get it updated.