Clear add schedule form between creation

What does this MR do?

A tiny MVC for: !60162 (comment 561018171) to clear the schedule form between adding schedules. We opt for the most boring solution possible is clearing with a simple method.

Screenshots (strongly suggested)

Merge	You are here
Allow for multiple schedule creation	!59829 (merged)
Add tooltip for add schedule button when feature flag is enabled	!60162 (merged)
Clear the schedule form between form creation	🤘
Abstract schedule action (modals) out of schedule loop to improve performance && only request open schedules	TBA
Update schedule create popover text (after EP are implemented) see: #273797 (comment 556382219)	TBA

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

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 feature is 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)