Resolve "Prevent accidental deletions via soft delete for groups" - db changes (MR: 1/n)

What does this MR do?

For #33257 (closed)

MR 1/n

I am splitting this feature into multiple MRs. This is the 1st MR which add necessary table and attributes for the deletion schedule.

Since we faced trouble in adding these attributes to the namespaces table directly, this is an alternative approach to create a new table to hold the deletion schedule details.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• 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