Add a "git expert"

[Jake-Pullen]

Is your feature request related to a problem? Please describe.
I'd love to get merlin help me with some git tasks. like writing a good PR detail. If he had the output of a git diff main then he should be able to give me a good description

Describe the solution you'd like
A new expert that can use git commands to provide context to the oracle.

Describe alternatives you've considered
hand feeding a diff into the chat and asking for a PR description

Additional context
?