label: add support for escalation policy, schedule, and rotation types

[mastercactapus]

Description:
Adds label support for escalation policies, schedules, and rotations.

Which issue(s) this PR fixes:
Part of #3403

Out of Scope:

• Searching by label for ep, schedules, rotations, will be done separately.

Describe any introduced user-facing changes:
N/A

Describe any introduced API changes:

• EP, schedule, and rotation types now have a labels field, similar to services
• create* for EP, schedule, and rotation now can pass in labels, similar to services
• setting labels now supports EP, schedule, and rotations as a target type

[tony-tvu]

Should we be able to create labels for escalation policy, schedule, and rotations on this branch? Since serviceID can't be null, I'm getting an error when trying to create a label for anything other than service labels.

[mastercactapus]

@tony-tvu oops, you're right; fixed in latest commit. You will need to make regendb though since it's a change in the migration

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.

[Forfold]

failed build deleted on CI, re-running to see failure

edit: looks like when editing a label, it is instead creating a new one on submit, resulting in the test failing because the page locator resolves to two elements.