[Feature Request] Support Alertmanager Webhooks in Cron Monitors

[lforst]

Discussed in getsentry/sentry-javascript#14909

^{Originally posted by alex-souslik-hs January 6, 2025}
Alertmanager sends POST HTTP requests with a specific JSON format as webhooks. This is incompatible with Sentry's monitor upsert API. Supporting those webhooks can allow using Sentry to monitor Alertmanager based pipelines via heartbeats, similarly to other Cron Monitor solutions.

[getsantry]

Routing to @getsentry/product-owners-crons for triage ⏲️

[evanpurkhiser]

I don't think we're going to support an alternative API format any time in the near future. What would probably work here for users who want to use Alertmanager webhooks is to have some light-weight proxy service to translate the webhooks into the cron check-in format.