Use the MR IID in the docs Review Apps URLs

What does this MR do?

We're taking advantage of the pipelines for merge requests https://docs.gitlab.com/ee/ci/merge_request_pipelines/.

This will result in a nicer URL which will be more informative than the previous one where a string of random characters was used.

• Before: review-docs-docs-84rudq
• After: review-docs-ee-4435

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This was previously opened in gitlab-foss!24360 (closed), but we hadn't enabled MR pipelines at that time.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content