FE for "Allow group owners to disable projects forking outside of GMA-group

What does this MR do?

Original issue: #202577 (closed)

This MR adds new toggle "Prohibit outer forks" to SAML Settings page

New toggle is displayed when :group_managed_accounts feature is enabled for the group, and could be enabled when group_managed_accounts setting is enabled

Screenshots

output

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done ty reports checked/validated by a reviewer from the AppSec team