[FE] Clean up pipeline execution policy code

Why are we doing this work

• in create the scheduled pipeline execution frontend code, follow-ups were saved for later

Relevant links

Non-functional requirements

• Documentation:
• Feature flag:
• Performance:
• Testing:

Implementation plan

• Sanitize values (Sanitize seconds value for schedule (!188526 - merged))
• Handle invalid types in schedule pipeline form (Update days property to an array (!188676 - merged))
• Follow-ups on monthly values (Allow users to reset all selections (!190441 - merged))
• Follow-ups for drawer (Update drawer to be more readable (!190443 - merged) and a couple of others)
• Follow-ups
• Update error shown for max number of schedule PEPs created (moved to Improve error on trying to create more than max... (#537763 - closed))
• Check split mode (Update timezone dropdown to update with new value (!190765 - merged))
• Add integration tests ([FE] Add integration tests (#541349 - closed))
• Add error exceeding max number (Improve error on creating Schedueled PEP with o... (#541357) because this is more work)

Verification steps