Support for multiple repos

[ejoncas]

Is there any reason why we don't support multi-repo? There's been a few opportunities already where I wish the PR description gets generated and points to PRs on other repos.

The .pr-train.yml could be moved somewhere centric as the user's home ~/.pr-train.yml

The different repos could be addressed in the same line using some sort of convention, or a more complex structure.

  my-awesome-but-complex-feature:
    - service-repo@ejoncas-TICKET-123-refactor
    - configuration-repo@ejoncas-TICKET-123-enable-prod
    - service-repo@ejoncas-TICKET-123-add-tests

Update: thinking this could get complicated to figure out what is your base branch.... as in the example the first 2 PRs would point to master but on different repos.