Add diff view for revisions on review page

[corneliusroemer]

While making some revisions on PPX I noticed how it was hard to check whether the changes were what I wanted them to be.

It would be very useful to have the submission review/approval page allow viewing a diff, similar to our released sequence version diff.

i.e. this page: https://pathoplexus.org/ebola-bdbv/submission/232/review should have something that has similar functionality to this page: https://pathoplexus.org/seq/PP_0079G2P.2/versions?compare=1%2C2

[claude]

This issue is related to #1945, which also addresses the challenge of making revision changes more visible on the review page. #1945 suggests highlighting changed fields, while this issue proposes a full diff view. Both aim to improve the UX for reviewing revisions by making changes more apparent to users.