Add support for GCP Alerts to create GitLab issue

Description

Add support for GCP Alert notifications to create GitLab issues.

Further details

Task list

• Create new cloud function gcp-alert-to-gitlab-issue
• This will pull basic information out out standard alert notification including documentation
• Ensure we only create issue for open events. Ignore close events
• Add environment variables for AlertEventHandler - similar to existing GKE_CLUSTER_UPDATE_AVAILABLE ones
• Add Terraform to configure env vars
• Ensure 100% unit code coverage

Acceptance criteria

• New cloud function
• Default issue configurations in Terraform should be based on Alert Documentation. This can be overridden if necessary
• 100% code coverage

Links/references

Use Alert support in gcp-pubsub-to-ms-teams as basis for this work.