Update on-call rotation time interval restrictions

What does this MR do?

Adds the frontend piece for adding and updating on-call rotation time interval restrictions.

The interval restriction consists of the 'Restrict to time intervals' checkbox as well as the associated time range. See screenshot below.

Changes:

• Data from the interval restriction field is now saved to the backend when adding a new on-call rotation.

Feature flag: :oncall_schedules_mvc

Issue: #262859 (closed)

• TODO: When !52998 (merged) is merged, rebase against and target the master branch.

Screenshots (strongly suggested)

New oncall schedule form

Note: No visual change - these UI elements existed previously but weren't connected to the backend.

Does this MR meet the acceptance criteria?

Conformity

• [n/a] Changelog entry
• [n/] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [n/a] 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
• [n/a] 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:

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