feat: allow --provider for all git commands (and add GIT_PROVIDER env)

[hojerst]

added --provider flag to all git repository based commands as those will fail otherwise when autodetection doesn't work (e.g. internal git repository)

[hojerst]

Fixes #290

[lblazewski]

I am not familiar with the codebase so I am not sure if this will work out but the changes look ok to me. Can any of the maintainers review the PR and check if we can get this in the next argocd-autopilot release?

I suspect that for many organisations running private gitlab instances which are trying out argocd-autopilot this would be a big decider 😄 Especially that the required changes (based on the PR) look relatively small.

Hope someone can tak a look ✌️

[jeremyj563]

The City of Davenport is one such organization that needs this feature 🙏 Thanks for this great tool and you guys rock!!

[noam-codefresh]

as i commented in #290 - the --provider is only required when creating a new repository (using provider api calls). not when performing any of the other operations (which are git-only, and provider-agnostic). please let me know if you think i should re-open this PR or the original issue.