Allow configuring defaults for celery-beat

### Problem Statement

Basically, I have the same request as [posted before](https://github.com/getsentry/sentry/issues/64881), I'd like to be able to configure these defaults for globally/per project.

As @gaprl writes in that post, many SDKs support these configuration options, which would be ok as well - but that doesn't seem to be the case for automatically-discovered celery-beat tasks, which is what I'm setting up at the moment. There's no mention in [the docs](https://docs.sentry.io/platforms/python/integrations/celery/crons/#celery-beat-auto-discovery). However, we can [configure that for manual monitors](https://docs.sentry.io/platforms/python/crons/#configuring-cron-monitors) and I tried adding `@monitor(monitor_config={...})` to auto-discovered tasks, but that didn't work.

Do I overlook something or is it indeed not possible to configure these values for auto-discovered beat tasks?

### Solution Brainstorm

Ideally we'd be able to configure global/project defaults. Failing that, configuring that via decorator in code would still be much preferable to manually configure each monitor via the Sentry web UI.

### Product Area

Crons

Start by comparing the Celery beat auto-discovery documentation with the manual cron monitor configuration documentation linked in the issue. Trace how auto-discovered tasks receive their monitor settings and verify whether decorator configuration is supported. Done means a defined way to configure defaults or decorators for auto-discovered tasks, with the behavior documented and tested.

Written by the indexing model from the issue text.