Feature: Enable the UI to operate with a local git repo only

This creates a local git repo and branch(es) for submissions. See the video for functionality.
This does not disrupt any existing functionality as it is only enabled with experimental mode turned on. Depends on #309 merging.
The git operations are server side renders as there is very little support for client side file system access outside of experimental support in chrome with showDirectoryPicker. Did not dig a great deal on this, just feels more sane to do it from the server side. The user will be running the server locally in this scenario or can run it as a service as desired as well.

TODO not necessarily on this PR:

[x] Author info needs to use the email since there is no GitHub ID that can be discovered. Also how does that square with the IL v2 spec.
[x] Dashboard needs to sort on date, not list the main branch and add more info/columns.
[x] Add an empty state with get started links for local actions.
[ ] Knowledge file handling (definitely a separate PR).
[ ] Determine what we call local mode in general. local is meh.

instructlab / ui