Resolve "Prevent accidental deletions via soft delete for groups" - API changes (MR: 4/n)

What does this MR do?

For #33257 (closed)

MR 4/n

I am splitting this feature into multiple MRs.

This is the 4th MR which adds necessary API endpoints to help perform

1. Mark a group for soft-deletion
2. Restore an already soft-deleted group to original state.

Changes here are similar to !18945 (closed), where we added similar API endpoints for project soft-deletion feature

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created - !19423 (closed)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database 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

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