Add props bot

[priethor]

Props Bot is a GitHub Action that processes the activity on a pull request and any linked issues.

The bot attempts to associate each GitHub user account with a linked w.org one and outputs a formatted list of Co-authored-by trailers that can be copied and pasted into the merge commit message.

This ensures that everyone who contributed to a given merge receives props for their effort, and that the list of contributors is predictably formatted for easy processing.

This bot is currently in many other repositories under the WordPress organization.

More details about the bot can be found in the original announcement post on the Make WordPress Core blog.

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Props to @desrosj , as this PR is a port from his previous implementations of this bot, like this.

[cbravobernal]

LGTM

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props priethor, cbravobernal.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.