Refactor behaviour of matching repo ids and branches in the server-side config

[dimisjim]

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• I'd be willing to implement this feature (contributing guide)

Describe the user story

I would like to be able to have a different behaviour of matching repo keys mentioned in https://www.runatlantis.io/docs/server-side-repo-config.html#repo, most importantly to be able to define the same repo id multiple times, but with a different branch regex each time. This way I can define something like this:

- id: github.com/org/repo1
  branch: /^prod$/
  workflow: prod
  allowed_workflows: [prod]

  autodiscover:
    mode: auto

- id: github.com/org/repo1
  branch: /^qa$/
  workflow: qa
  allowed_workflows: [qa]

  autodiscover:
    mode: auto

- id: github.com/org/repo1
  branch: /^dev$/
  workflow: dev
  allowed_workflows: [dev]

  autodiscover:
    mode: auto

which would match the repo selector that contains the most matches. Thus if repo1 is matched, it will only match the dev branch, only if it is the last occurrence, as it is above, but if it was first or second in the list, it wouldn't match at all.

Describe the solution you'd like

For example, if repo is matches AND branch is matches, stop there, and do not pick a later repo occurrence as mentioned in the doc link above: "If multiple repos match, the last match will apply."

Describe the drawbacks of your solution

This is a completely different behaviour than the one currently in place. Maybe an extra flag which allows you to pick the current one or the one proposed here would be nice, or actually essential, to have.

Describe alternatives you've considered

Do this configuration in the repo level config, by defining multiple projects