Allow generic alerts to set gitlab environment

What does this MR do?

This adds the ability to associate a [non-prometheus] AlertManagement::Alert with an Environment.

By providing the gitlab_environment_name in the Payload, we will attempt to match an environment for the project by the given name, and associate that to the Alert. This variable name matches the existing name we use for Prometheus alerts (https://docs.gitlab.com/ee/operations/metrics/alerts.html#external-prometheus-instances).

Note: Prometheus alerts are already able to be associated via the Prometheus Alert (metric alert), or in External instances using the same key in the labels object of the alert payload. See https://docs.gitlab.com/ee/operations/metrics/alerts.html#external-prometheus-instances

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #238485 (closed)