Add CRON interval mechanism and modal to /pipelines page

Merge Request Checklist

• Link to an issue
• Include the proposed fix or feature
• Include and update tests for the modified code
• Include a documentation change
• Add a CHANGELOG.md entry in the Unreleased section for any user-facing changes
• Mention or assign a maintainer

Closes #2528 (closed) #2527 (closed)

Below is a screen recording of a new UI feature. Now it will be possible to utilize CRON jobs in the UI (like you can in the CLI).

Screen_Recording_2022-02-25_at_11.59.47_AM