Improve viewer for suppressed files in merge requests

Problem to Solve

When suppressing diffs via .gitattributes it's not possible to actually load the diff if you do want to review the file. You're presented with a message like:

Additional Details

Suppressing diffs via the .gitattributes file by setting something binary is a hack, but we could still make this experience better for manual suppression.

Proposal

The viewer message should be updated to specify that the file was suppressed because of .gitattributes (as opposed to or unsupported encoding). We should also provide a link to load the diff anyway which would then retrieve the correct diff and apply all the markup required to display it for the user.