Support for other types of repos for the PR script

[jtpio]

Problem

At the moment the PR script runs the following command which is specific to Python repos:

maintainer-tools/pr_script.py

Line 52 in 90bc268

run("pip install -e '.[test]'")

Proposed Solution

This could be similar to the jupyter_releaser choosing which command to run based on the existence of pyproject.toml / setup.py / package.json.

Additional context

This would make the PR script more generic.