Adjust group sharing settings for restricted access and user cap

Resolves Stop disabling project sharing within the same ... (#488451 - closed).

What does this MR do and why?

When seat controls are enabled (user cap or restricted access), GitLab was automatically enabling two settings:

1. prevent_sharing_groups_outside_hierarchy - Prevents inviting groups from outside the hierarchy
2. share_with_group_lock - Prevents sharing projects with all groups (internal or external)

This MR changes the behavior to only automatically enable prevent_sharing_groups_outside_hierarchy, while allowing share_with_group_lock to be independently configured.

References

• Stop disabling project sharing within the same ... (#488451 - closed)
• Restricted Access GA (&12452)

Screenshots or screen recordings

Before	After

How to set up and validate locally

User cap

1. Create a test group
2. Go to Settings > General > Permissions and group features
3. Under "Seat control", select "Set user cap" and set any value
4. Press "Save changes"
5. In "Permissions", verify:
   • "Members cannot invite groups outside of <group> and its subgroups" is checked
   • "Projects in <group> cannot be shared with other groups" is unchecked
   • You can manually check or uncheck "Projects in <group> cannot be shared with other groups" and it persists

Restricted access

1. Ensure your test group has a paid subscription
2. Go to Settings > General > Permissions and group features
3. Under "Seat control", select "Restricted access"
4. Press "Save changes"
5. In "Permissions", verify:
   • "Members cannot invite groups outside of <group> and its subgroups" is checked
   • "Projects in <group> cannot be shared with other groups" is unchecked
   • You can manually check or uncheck "Projects in <group> cannot be shared with other groups" and it persists

MR acceptance checklist

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