Set a rel:canonical on moved issues to point to their new location

Problem:

On public projects an issue that's been moved gets a new URL (example: gitlab-org/gitlab-foss/-/issues/48761 moved to /gitlab-org/gitlab/-/issues/23080). Both pages will continue to exist and Google will index both causing confusion for users searching for the title/description.

Solution:

Set a rel:canonical on the 'moved' issue to point to it's new location | Google's documentation here. This will solve the duplicate indexation issue and make it easier to search for moved issues on google.