Related to https://github.com/grafana/oncall-private/issues/2994
- Extend gaps/empty shift checks to consider 30 days (customizable via
param, eventually make it customizable per schedule?); ie. every week
(per beat schedule), check the schedule next 30 days
- Trigger checks via async task on schedule API updates (instead of a
sync call)
- Update notifications wording / link to schedule
# What this PR does
Follow up PR to https://github.com/grafana/oncall/pull/5199 and
https://github.com/grafana/oncall/pull/5224, addresses a few issues I
noticed on dev while testing the feature
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
show up in the autogenerated release notes.
