jujutsu: add ediff option

[bbigras]

based on https://github.com/martinvonz/jj/wiki/Emacs#ediff-as-a-merge-tool

Description

Checklist

• [x] Change is backwards compatible.

• [x] Code formatted with ./format.

• [x] Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• [ ] Test cases updated/added. See example.

• [x] Commit messages are formatted like

  {component}: {description}
  
  {long description}

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • [ ] Added myself as module maintainer. See example.

Maintainer CC

@shikanime

[bbigras]

@rycee thank you very much for the suggestions. It does seem to work.

[rycee]

Looks good. Merged to master now 🙂

[bbigras]

Thanks!