Add gitops app config fields, API access, activities, tests (#26282)

## For #26230 

- Add `gitops` settings to app config
- GET and PATCH endpoint functionality to retrieve and modify these
settings
- generate activities for enabling and disabling GitOps mode
- Premium only
- Update tests

<img width="1355" alt="Screenshot 2025-02-17 at 9 22 13 AM"
src="https://github.com/user-attachments/assets/e03d7fd6-8795-4df2-9c8f-ffbcabd2d212"
/>

<img width="1575" alt="Screenshot 2025-02-17 at 9 24 33 AM"
src="https://github.com/user-attachments/assets/5bf963d4-6fb7-4586-8f6f-9e605c25bf06"
/>

## Checklist for submitter

- [x] Added/updated automated tests
- [ ] A detailed QA plan exists on the associated ticket (if it isn't
there, work with the product group's QA engineer to add it)
- [x] Manual QA for all new/changed functionality

---------

Co-authored-by: Jacob Shandling <jacob@fleetdm.com>

tools/cloner-check/generated_files/appconfig.txt

@@ -175,6 +175,9 @@ github.com/fleetdm/fleet/v4/pkg/optjson/Slice[github.com/fleetdm/fleet/v4/server
 github.com/fleetdm/fleet/v4/server/fleet/MDMAppleVolumePurchasingProgramInfo	Location	string
 github.com/fleetdm/fleet/v4/server/fleet/MDMAppleVolumePurchasingProgramInfo	Teams	[]string
 github.com/fleetdm/fleet/v4/server/fleet/MDM	AndroidEnabledAndConfigured	bool
+github.com/fleetdm/fleet/v4/server/fleet/AppConfig	UIGitOpsMode	fleet.UIGitOpsModeConfig
+github.com/fleetdm/fleet/v4/server/fleet/UIGitOpsModeConfig	GitopsModeEnabled	bool
+github.com/fleetdm/fleet/v4/server/fleet/UIGitOpsModeConfig	RepositoryURL	string
 github.com/fleetdm/fleet/v4/server/fleet/AppConfig	Scripts	optjson.Slice[string]
 github.com/fleetdm/fleet/v4/pkg/optjson/Slice[string]	Set	bool
 github.com/fleetdm/fleet/v4/pkg/optjson/Slice[string]	Valid	bool