feat: add pr_number as an optional output on the action

[jpower432]

Description

Adds the pull request number as an output of the action for further steps in workflow to facilitate automation like assigning reviewers or making comments.

Type of change

• New feature (non-breaking change which adds functionality)

How has this been tested?

• Update unit tests
• Integration test w/ GitHub Actions: TODO

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules