Implementing Label Assignment on Schedules, Escalation Policies, and Rotations

[mastercactapus]

What problem would you like to solve? Please describe:
Currently, GoAlert allows the assignment of labels to services for easy searching and grouping. Lets expand this functionality to schedules, escalation policies, and rotations.

Describe the solution you'd like:
Extend the label assignment functionality to schedules, escalation policies, and rotations. This will enable better grouping and searching of related resources in GoAlert.

Implementation:

1. Add a labels attribute to the Create calls for these resource types
2. Add the new target types to the setLabel mutation
3. Update the search queries to support labelkey=value as a label search

Describe alternatives you've considered:
N/A

Additional context:
The primary use case for this feature would be updating GoAlert configuration by API (as opposed to manually in the UI), where labels could group related resources. Additionally, the current implementation was designed with this extension in mind, which can make this enhancement more achievable.