PR Template based on folder #1654

Additionally to pull_request_template.md (and the ones that can be achieved with custom URL parameters), it would be beneficial to be able to create PR templates based on folder (or even file).

So proposal is to either:

1. Allow .github folder in subfolders of a repository with own pull_request_template.md files
2. Or structure the templates under .github folder according to the repository structure

When a pull request with changes to multiple folders (or files) comes in, the PR templates are gathered together as the basis of the PR comment. This would allow people to concentrate only to the things that matter to the actual change (test vs. implementation, different libraries for example might have different needs from the PR templates, etc.).