This PR takes the localization features out of "experimental" to prep
for the announcement
- rename settings and gives them its own area
- `experimental_content_localization` to `content_localization_enabled`
- `experimental_content_localization_allowed_groups` to
`content_localization_allowed_groups`
- `experimental_content_localization_supported_locales` to
`content_localization_supported_locales`
- `experimental_anon_language_switcher` to
`content_localization_anon_language_switcher`
- migration
- related to discourse/discourse-ai#1439

| screenshot 📸 |
|---|
| <img width="964" alt="Screenshot 2025-06-17 at 5 06 32 PM"
src="https://github.com/user-attachments/assets/9a8b2c38-c846-4fc9-8ddd-815c45cc3d0e"
/> |