After #52953 gets merged the git graph will be ready for it's preview
release, so we can finally remove the feature flag! AKA this PR releases
the git graph

Self-Review Checklist:

- [ ] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- Add Git Graph. Can be accessed through the button on the bottom of the
git panel or the `git graph: Open` action