Frontend: Enable/Disable group secrets manager

Why are we doing this work

Add the UI for enabling and disabling the group secrets manager. This should function similarly to the toggle for the project secrets manager.

Implementation table

header	header
backend	#577340
frontend	👈 You are here!

Implementation plan

The toggle for the project secrets manager lives in Settings > General > Visibility, project features, permissions, but this doesn't exist in the group settings. We can instead add the setting in Settings > General > Permissions and group features.

The UI behavior for project and group secrets manager toggles should be the same. Refer to the code in ee/app/assets/javascripts/pages/projects/shared/permissions/secrets_manager/secrets_manager_settings.vue.

Verification steps

1. Upload a Premium license (or above).
2. Set up openbao on your gdk.
3. Enable the secrets_manager_group feature flag.
4. Go to your Settings > General > Permissions and group features in your group and toggle the group secrets manager.