PR template selection #3593

<!-- 1. Make sure your requested feature makes sense for Refined GitHub: https://github.com/sindresorhus/refined-github/issues/2960 2. Include a full URL where the feature should appear. -->

It would be awesome to have a dropdown on the PR creation page to select from multiple PR templates, just like you can with issue templates.

You can currently select a PR template by appending it to the URL as a query param (?template=template_name), but that's not user-friendly at all, and gives no info about what PR templates exist. This is in stark contrast to the template selection page when creating a new issue.

I know a new page to mimic issues doesn't fall into the feature guidelines for Refined GitHub, but a dropdown would serve the same purpose and likely be much easier to implement

Example URL where the feature should appear: https://github.com/sindresorhus/refined-github/pull/new/hotfix

There is an existing extension to do this (https://chrome.google.com/webstore/detail/github-pr-template-picker/foaaibihjfcacpiehnjaghlhopofmmnb?hl=en-US), but it's chrome-only and unmaintained since 2016. I couldn't find any userscripts that did something similar