feat: Output markdown as Step Summary and Text, and Optionally Output PR comment

[Kludgy4]

Motivation

Warning

This is a duplicate of #34 because I've never used github fork/sync before and wiped my changes, which closed the previous PR. This is a recovery, improvement, and refiling of that PR.

Supports non-pr use cases by outputting raw markdown as output. Make "commenting" optional as well.
Always output markdown into GITHUB_STEP_SUMMARY.

From my testing the standard PR commenting behaviour appears to be unchanged when the action is triggered by a pr.

Changes

• The generated markdown is now always output from the action in:
  • Full raw output per Unable to use output outside of a pull request context #33
  • A Github Step Summary per idea: Support for adding to the summary page of a workflow run #13.
• The action now detects whether it was triggered by a PR, and only attempts to create a PR comment if true

Example Use Case

Here is an example of me using this adjusted action to output markdown into a GITHUB_STEP_SUMMARY (not a comment!) before a job that requires environment-specific approval.

[Kludgy4]

@borchero have followed up on your feedback for your review :)

[borchero]

This looks great already, thank you! I left a couple suggestions :)

[borchero]

Thank you for the updates, I think we're almost there! 🚀

One more request: could you introduce a parameter skip-comment to the action (and document it in the README)? This would allow people to only use the summary if they want and would finally allow me to fix the CI for pull requests (as forks cannot create PR comments...).

[Kludgy4]

@borchero resolved your previous comments for you to look at