Fix: Do not clear rotation form on validation error

What does this MR do?

A tiny MVC for: #324688 (closed) where do not clear the rotation form unless you are adding a new rotation or have successfully submitted the form to allow for validation errors. We do this by updating the logic for the @hide and @show logic slightly to be gated.

How/What to test

This feature needs the minimal license is GitLab Premium 👀

To validate this merge:

• Navigate to Operations => On-call Schedules or direct link is your_project/-/oncall_schedules e.g. http://127.0.0.1:3000/gitlab-org/gitlab-shell/-/oncall_schedules.
• Click "Add schedule on empty state"
• Add a base schedule
• Click "Add a rotation"
• Add a base rotation with any name
• Attempt to create a new rotation with the same name
• The form should not clear when you get the error but should clear if you elect to add a new rotation

Screenshots (strongly suggested)

Before	After

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Related to #324688 (closed)