Allow generic alerts to get Gitlab Enviroment

We currently let Prometheus Alerts to specify their GitLab Environment by providing the gitlab_environment_name variable in the payload https://docs.gitlab.com/ee/operations/metrics/alerts.html#external-prometheus-instances.

We should allow this for regular non-prometheus alerts too.

By having an alert associated to an environment, it will allow us to provide context to the alert:

• Associate a deployment to an Alert
• Allows grouping or filtering of Alerts by Environments (i.e provide ability to ignore dev alerts)

~"group::health" devopsmonitor backend featureaddition