Multiple Schedules - load one rotation set at a time

What does this MR do?

A small MVC for #273797 (closed) where we limit the rotation shift query to only when the schedule cards are opened by leveraging the skip hook. We also default to only open the first schedule card on the initial page load for performance.

Merge Train

Merge	You are here
Allow for multiple schedule creation	🤘
Add tooltip for add schedule button when feature flag is enabled	!60162 (merged)
Clear the schedule form between form creation	!60417 (merged)
Only request open schedules to improve performance	🤘
Abstract schedule action (modals) out of schedule loop	TBA
Update schedule create popover text (after EP are implemented) see: #273797 (comment 556382219)	TBA

Screenshots (strongly suggested)

No feature flag	feature flag enabled

How to test this?

1. Enable the feature flag => ❯ echo "Feature.enable(:multiple_oncall_schedules)" | rails c
2. Ensure you are at least a project maintainer and have a GitLab Premium license running.
3. Navigate to On-call Schedules for any project => Operations > On-Call Schedules http://localhost:3000/h5bp/html5-boilerplate/-/oncall_schedules
4. Test CRUD for multiple schedules
5. Test CRUD for multiple rotations per schedule created
6. See the rotations are only requested for open schedule cards

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 merge sits behind a feature flag .
• [-] 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
• [-] 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 #273797 (closed)