feat: implement gitleaks

[loispostula]

closes https://github.com/ForesightMiningSoftwareCorporation/infrastructure/issues/122

[greaka]

We need to watch out. Github only allows 20 custom workflows in one run, and we are getting close to the limit. So this would probably be one of the first workflows that we will break up eventually.

[loispostula]

Can you point me to the doc stating that limit?

[greaka]

Here you go: https://docs.github.com/en/actions/using-workflows/reusing-workflows#limitations

[loispostula]

Ah indeed, I was planning on enabling this workflow through required workflowsd, so it would not be a reusable workflow