[feature] Write octodns-sync plan to pull request comment

[solvaholic]

fixes #35

How to test with the changes in this pull request

Use solvaholic/octodns-sync@issue35 to run the changes pushed to branch issue35:

• Add an html output to your plan_outputs in your octodns config, for example in public.yaml:

  manager:
    plan_outputs:
      html:
        class: octodns.provider.plan.PlanHtml

• Configure your workflow to enable add_pr_comment and provide a token:

  on:
    pull_request:
  jobs:
    test:
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v2
        - uses: solvaholic/octodns-sync@issue35
          with:
            config_path: public.yaml
            add_pr_comment: 'Yes'
            pr_comment_token: '${{ github.token }}'

To-do list

• Document feature in README
• Document changes in CHANGELOG
• Save octodns-sync log and plan output to two separate files
• [ ] Expose those ☝️ file paths as action outputs
• Add action inputs to enable feature and to define an API token
• Add octodns-sync plan as a comment to the triggering pull request when:
  • GITHUB_EVENT_TYPE is pull_request
  • Input add-pr-comment is "Yes"
• What changes are required for run local option?
• Provide example configs for different usage scenarios?

[solvaholic]

Expose those ☝️ file paths as action outputs

I changed my mind, would like to do this step in a separate pull request. It's unnecessary for this feature and it'll require changes to entrypoint.sh (and, therefore, the Docker image).

[solvaholic]

For posterity: This block looks the way it does, here, because it was the first way I found to meet these constraints:

• Use the add an issue comment API with a provided personal access token
• Get $_body into the JSON payload ~safely
• Do not install gh or curl
• Do not introduce dependencies, for example an external Python script or package

[solvaholic]

What changes are required for run local option?

None.

Provide example configs for different usage scenarios?

I added to README.md to cover available features.

[solvaholic]

I'll go ahead and merge this into main. Manual tests went fine and the new feature is disabled by default.

[xt0rted]

@solvaholic are you planning on doing a new release with these changes or are you waiting until the feedback I had is addressed? Right now I'm pinning to a4b4942 and did my first deploy Friday. It worked great, thanks again for the great action.