FE [Group owner bypass] Integrate form with backend

This requires the backend for group owner bypass confirmation to be merged:

• #534329 (closed) - adds bypass column
• #540573 (closed) - process expiry date backend, incl adding column

This is a follow up issue to #544024 (closed) which added a checkbox and expiry date picker to the group/settings page.

The outstanding work

• bind the expiry date to the column created by the backend
• Expiry date is required when the checkbox is checked
• determine whether the expiry date should be disabled or hidden when the checkbox is disabled.
• Premium badge feature - would that require a subsection heading?
• Update docs. See guidance !189546 (comment 2503128087)

Use feature flags group_owner_placeholder_confirmation_bypass

Summary of feature (once complete)

The checkbox should be shown for all top-level groups on GitLab.com, but in disabled state on Free tier (unable to click the box). On Premium and Ultimate in enabled state (i.e. user can change the setting).

• Only show the settings for top-level groups AND when GitLab.com (Group#root? plus Gitlab.com? or Gitlab::SaaS.feature_enabled? check)
• Only enable the setting if the top-level group can configure a verified domain (#domain_verification_available? check which checks their license tier, that they're a top-level group, and that they're on GitLab.com).

We only allow the enterprise bypass when all of these criteria are met:

• Feature flag is enabled AND Group has the setting enabled AND has correct license tier AND user is one of their enterprise users AND it's GitLab.com AND group is top-level group.