Automate issue creation for when Repository X-ray worker errors exceed a certain threshold

Context

As part of #517181 (closed), we set up alerts for when Repository X-ray worker errors exceed a certain threshold.

For the second component, we want to automate an actionable issue creation similar to #517173 (closed) (with priority labels) when these alerts are triggered so that our team can take action on it as soon as possible.

There are some ongoing discussions that may be useful as reference points:

• gitlab-com/gl-infra/observability/team#4013
• Slack

Desired outcome

• Actionable issues (with priority labels) are automatically created when ScanDependenciesWorkerHighErrorRate alert is triggered
• Automation setup process documentation for future reusability

Relates to:

• #517181 (closed)
• gitlab-com/runbooks!8510 (merged)
• gitlab-com/gl-infra/observability/team#4013