Link merge request dependencies errors to docs
Problem to solve
In Zendesk #354680(Internal only) the customer suggested that the cause for merge request errors is not easily found.
The suggestion is to add a link pointing to the docs.
Proposal
Add a link to the docs in the error message. The docs already explain why the errors appear and point to the issue where we track the work being done to enhance this functionality.
Error text should read:
Failed to save: Dependency chains are not supported. Learn more.
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