Add pre-commit configuration

[lucacome]

Proposed changes

Adds configuration for pre-commit.com that runs checks automatically before committing and (in most cases) fix the problems.

Here the quick start for installing it, basically:
brew install pre-commit followed by pre-commit install. After that, it will run before every commit.

I've added some hooks in the config (there are many more):

golang-ci lint and prettier, which we're already using, will just run it automatically
pre-commit-hooks, has a few hooks, mostly about formatting (and end of line whitespaces and similar), and not committing large files or with merge conflicts.
gitleaks, for detecting and preventing hardcoded secrets like passwords, api keys, and tokens in git repos.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[ciarams87]

🚀

[kate-osborn]

Thanks for doing this @lucacome!

Can you add the pre-commit installation instructions or link to the quickstart installation list: https://github.com/nginxinc/nginx-kubernetes-gateway/blob/main/docs/developer/quickstart.md#setup-your-development-environment?

[pleshakov]

are we going to enable this in the CI too?

[lucacome]

@kate-osborn I added the docs 👍

@pleshakov once this PR is merged I will enable the pre-commit CI for the repo. It's an app that we have installed for the org that runs the checks, commits fixable changes and keeps the dependencies up to date.