Add a link to the "Added N commits" note like "Compare with previous version"
As referenced in https://gitlab.com/gitlab-org/gitlab-ce/issues/22721, and as initially suggested in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6127#note_15003712.
With the new Merge Request Versions feature, the automatic "Added N commits" system note, which is created on every push to an MR, should have a link to show the changes between the new push and the previous one (i.e. to compare it with the previous version).