Allow user to specify octodns ref to run

[solvaholic]

Description

• Resolves Support using unreleased versions of octodns #50
• Removes Docker container and image dependencies
• Configures action to run on the Actions runner directly

Motivation and Context

To facilitate the request in #50, primarily.

I think moving from the Docker image to the runner scripts gives better flexibility and extensibility, and makes this action a much less complex addition to a workflow.

How Has This Been Tested?

No testing, yet. Manually, running this action @issue50 from repos holding configs.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• All new and existing tests passed.

Changes

• Add changelog entry
• Update README
• Remove files that were only there to support using Docker image and container
• Rewrite action.yml to use scripts rather than container
• Create scripts
• Remove dockerlint from linter.yml

[] Update release.yml and docs/release.md (goto #55)

[solvaholic]

Using this syntax I demonstrated the current version of this action a) runs and b) will update the pull request as-configured:

      - name: Test current configuration
        id: octodns-test
        uses: solvaholic/octodns-sync@issue50
        with:
          config_path: test-config.yaml
          doit: 'no'
          add_pr_comment: 'Yes'
          octodns_ref: ${{ steps.pick-ref.outputs.octodns_ref }}
          pr_comment_token: ${{ secrets.PAT }}

So far, so good. Before merging I'll run more tests and make sure --doit works too. If that's in a public repository I'll link it here.

[solvaholic]

--doit tested OK in a private repo, tho #51 freaks me out every time I notice it happening. Also spotted #57 while testing.

I'll go ahead and make v2.1.3 from be7cf5b, then merge this PR to update main.

#57 cannot impact anyone currently using main, since the octodns_ref input doesn't exist yet there. It can only hurt when octodns_ref is set to a branch name - if octodns_ref matches a version tag install.sh will use pip install which will avoid the issue.