issue-289 feature: add pr-number optional input

[dalevfenton]

This PR proposes a fix for #289

Changes:

• adds a prnumber optional input that can be populated so the action can lookup a Pull Request if it is not in the action context
• if prnumber finds a Pull Request it will use that to lookup and either create or overwrite the report comment as well as checkout the base branch and run coverage difference report.
• updates tests for new shape of Options and using the pull_request data set there instead of in the context
• adds section in README to describe usage

How To Test:

• create an action that uses the push event
• populate prnumber with gh-find-current-pr action output
• open a PR, expect to see coverage run and comment created including with coverage diff
• push another commit, expect to see the comment updated

[ArtiomTr]

Hey @dalevfenton 👋,

Thank you for your work! Sorry for the delay. I didn't have enough time to review your PR. Everything looks perfect, but some tiny changes are required.

[dalevfenton]

@ArtiomTr updated PR with your requested changes, added a couple test cases and updated the README

[ArtiomTr]

LGTM

[ArtiomTr]

Thank you for your contribution!

[ArtiomTr]

@all-contributors please add @dalevfenton for docs, code

[allcontributors]

@ArtiomTr

I've put up a pull request to add @dalevfenton! 🎉

[ArtiomTr]

@dalevfenton These changes are published under the v2.0.9 tag.