Rename and restructure

[zdrve]

Rename the repository to check-codeowners (I have created https://github.com/zendesk/check-codeowners to reserve the name until we do this).

Provide a second GitHub Action, to actually perform the check, not just install the script.

It would be nice if these both were valid:

Install, then run:

    - name: Install the check-codeowners script
      uses: zendesk/check-codeowners/install@v123
    - name: Check codeowners
      run: check-codeowners --strict --find-no-matches --check-unowned

Run, without installing:

    - name: Check codeowners
      uses: zendesk/check-codeowners@v123
      with:
        options: --strict --find-no-matches --check-unowned

or even:

    - name: Check codeowners
      uses: zendesk/check-codeowners@v123
      with:
        strict: "true"
        find-no-matches: "true"
        check-unowned: "true"

(though that last variant then makes it hard to know what command one may run at the shell, in order to match what the action does. Perhaps in this case the action could print the equivalent shell command to stderr).

[zdrve]

cc @grosser

[grosser]

yeah v2 is nicest 👍

[grosser]

... but v1 is good enough and easy to copy-paste 🤷