[Feat]: Speed up the git status part of the git attestor

[matglas]

Describe the solution you'd like:

The current part that is capturing the git status in the git attestor is slow especially when using a large repository. Go-git does not do threading and capturing the status takes a long time because of that.

User value:

By improving the speed users with larger repositories will see a significant speed up in the execution time of witness. This plays a part in adoption. As a DevOps engineer I want to keep my pipelines fast but I do want to capture attestations with Witness.

Expected behavior:

Status should be captured as fast as doing a normal git status on a repo.

Proposed solution:

Replace go-git or use git cli as a hybrid solution to capture the status of the repo in the attestation.

Testing changes required:

TBD

Documentation changes required:

TBD

[matglas]

I think this might be an enhancement. But we can't set labels and this template worked the best 😄
@jkjell can you adjust this?