Add the golangci-lint GitHub action

[wallrj]

Run golangci-lint as a GitHub action, to provide fast feedback to a PR author about various common mistakes that are found in their code.

Initially we enable only one linter and check only G112.
The idea is that other checks and linters can be enabled one-by-one in separate PRs.
Each PR will enable only one new check and fix any offending code.
This way, the PRs are easy to review
and easy to cherry-pick into previous release branches if the fixes are deemed important enough.

Eventually, when all standard linters and checks have been enabled, the non-standard file .golangci-lint.*ci*.yaml can be renamed to .golangci-lint.yaml so that it developers can simply run golangci-lint run . locally (or via their editor / lsp-server) and get feedback before even creating a PR>

The advantages of running golangci-lint via a GitHub Action vs running it via prow + make target, are:

1. Performance: The GitHub action has been optimized to report as fast as possible, by careful caching and parallelization: https://github.com/golangci/golangci-lint-action#performance. It is possible to achieve the same results via Prow but it would take time and effort to achieve and maintain.
2. Web UI: Any failures are reported as GitHub Actions annotations which show up alongside the code changes in each PR. This makes it very easy to see what code needs changing. It would not be possible to achieve this using Prow.

The disadvantages are:

1. The cert-manager maintainers will need to have expertise in Prow and GitHub Actions.

Instances of G112 have already been fixed in a another PR:

• Mitigate potential Slowloris attacks by setting ReadHeaderTimeout in all http.Server instances #6534

NONE

/kind cleanup

[wallrj]

/kind cleanup

[wallrj]

/hold until discussed with other maintainers.

[maelvls]

Hey, I am very happy that we are finally going to try this approach. As long as people interacting with the project are able to quickly figure out how to run the same checks locally (documentation or make command), I am totally OK having linters and checks outside of Prow.

/lgtm
/hold if someone else wants to review

[inteon]

I agree, combining GH with prow is no big deal.
Having said that, if someone wants to move this to make; I would approve that PR too.
/unhold

[maelvls]

/approve

[jetstack-bot]

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