[CI] Add go fmt check

[djaglowski]

See #11432

Our CI process is currently not ensuring that go fmt has been run.

[mx-psi]

I believe go fmt is checked by golangci-lint

opentelemetry-collector-contrib/.golangci.yml

Line 113 in f33bba3

- gofmt

[djaglowski]

Hmm, if I'm understanding this correctly, then make gofmt includes all *.go files regardless of build tags, whereas the linter does not.

[mx-psi]

Hmm, if I'm understanding this correctly, then make gofmt includes all *.go files regardless of build tags, whereas the linter does not.

Okay, yes, I think that's the case. Still, this doesn't feel like a problem specific to go fmt: it happens with all linters that we run as part of golangci-lint, right? The only difference is that gofmt can run on all files regardless of build tags, while other linters probably can't.

I guess this is an easy solution for go fmt, just wondering if the 'correct' solution is to run golangci-lint multiple times with different build tag combinations.

[djaglowski]

I think you're probably right that making the change at the golangci-lint level is the more correct solution. I haven't had time to look into this further though, so I've captured it in an issue and will close this PR for now.