monitoring: add observability.alerts support for sourcegraph/server
Created by: bobheadxi
Stacked PR on top of https://github.com/sourcegraph/sourcegraph/pull/11832. Adds support for the functionality added in the above PR to sourcegraph/server
Closes #11473, closes #11612
VERSION=dev IMAGE=sourcegraph/server:dev cmd/server/build.sh
IMAGE=sourcegraph/server:dev dev/run-server-image.sh