ollama: add module

[terlar]

Description

This adds the service ollama, based on the corresponding NixOS module

It skips some of the options that doesn't make sense for the user unit and of course work with the Home Manager systemd.user.services which is slightly different.

Fix #5152

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.

• [x] 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

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

Maintainer CC