🚀 Feature: Allow filtering on PR author

[JoshuaKGoldberg]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Right now, prune-github-notifications allows filtering on reason and title. But sometimes an individual will send a PR that just so happens to look like a bot's PR. It'd be nice to be able to filter to just the PRs sent by the bot. A couple of example use cases:

• author: [/^dependabot[bot]$/]: would work for many straightforward repos
• author: [/^SomeUser$/, /[bot]$/]: would ignore one user and all bots

Let's add in an --author CLI option & author Node.js option!

Additional Info

No response