Add Require user password to approve to group-level MR approval settings

What does this MR do?

Adds the Require user password for approvals checkbox to the group MR approval settings. It adds the checkbox to the settings Vue app and to the store, as well as updating the specs to include the checkbox and also cover more of the view.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because this is behind the group_merge_request_approval_settings_feature_flag feature flag.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

1. Enable the feature flag group_merge_request_approval_settings_feature_flag via the rails console
2. Go to a groups settings [GDK_HOST]/groups/[GROUP]/-/edit
3. Expand the Merge request approvals section
4. Test the checkbox gets set/unset and shows the correct value on refresh

• 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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related to #247904 (closed)