Before this PR you could only have the git graph open for the active
repository, this PR changes that.
So you can have 1 git graph open per repository, allowing you to open
multiple different graph at the same time.

**Example**:


https://github.com/user-attachments/assets/9775108f-826a-476f-95de-46abcc1777a6

**Example Persistence**


https://github.com/user-attachments/assets/dbcf6692-7a67-46d9-a7ae-43a7c9a35818

Before you mark this PR as ready for review, make sure that you have:
- [x] Added a solid test coverage and/or screenshots from doing manual
testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

cc @Anthony-Eid I removed the switch repo test since it's no longer a
thing.

Release Notes:

- N/A

---------

Co-authored-by: Anthony Eid <hello@anthonyeid.me>