git: Add an onboarding and banner flow (#26518)

TODO:

- [ ] Hide the reset onboarding action (only useful for development,
uncomment:
https://github.com/zed-industries/zed/pull/26518/files#diff-f0ce01d9a3df30f60c64b6f9906c54aa0191246a58dbf5297ee321575a180879R96)
- [x] Get a designer to replace the modal background (@danilo-leal)

Release Notes:

- Added a small onboarding banner for the git launch

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: Danilo Leal <67129314+danilo-leal@users.noreply.github.com>

crates/git_ui/Cargo.toml

@@ -21,7 +21,9 @@ anyhow.workspace = true
 askpass.workspace = true
 assistant_settings.workspace = true
 buffer_diff.workspace = true
+chrono.workspace = true
 collections.workspace = true
+command_palette_hooks.workspace = true
 component.workspace = true
 db.workspace = true
 editor.workspace = true