UI: Add Service-level Rules page and Rule create/edit form

[tony-tvu]

Problem Description: The go-signal branch contains a lot of backend work that has been done, but there is no UI for it yet. This makes it difficult to test and use the new backend functionality.

Proposed Solution: Add UI features to create, edit, and delete service rules (POC).

Additional Context: Part of https://github.com/target/goalert/issues/3318