Resolve "Add a cop to ensure a correct merge request link"

What does this MR do and why?

In this merge request, we are adding a new cop to validate the introduced_by_url url (batched background migrations dictionary).

We need to have this link in the proper format because we will have a job that will extract the merge request ID from the link. More info here: gitlab-org/database-team/gitlab-com-database-testing!172 (comment 1658600386)

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How to set up and validate locally

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MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #432943 (closed)