Add pipeline schedules pagination

What does this MR do and why?

Adds schedules pagination for self managed instances where schedules count can be over 100.

Related to: #426141 (closed)

Screenshots or screen recordings

Screenshot has changed limit to 3 per page in app/assets/javascripts/ci/pipeline_schedules/constants.js for testing.

How to set up and validate locally

1. Have pipeline schedules created
2. Change SCHEDULES_PER_PAGE variable to value lower than total count to invoke pagination.
3. Test to ensure pagination works visit Build > Pipeline Schedules
4. Review code

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.