build: label PRs with GitHub Action instead of nodejs-github-bot

Main goal of using a GitHub Action for labelling PRs has been to move
the mapping between files changed -> label into a configuration file
local to the nodejs/node repository.

Previously any changes to that mapping meant having to grasp the
nodejs/github-bot project, open a PR with the neccessary changes, get
approval from its maintainers before those changes finally got pushed
to production.

The logic involved in using the file paths / label configuration and
resolving the labels to be applied, has been moved into a custom GitHub
Action project: nodejs/node-pr-labeler.

Aside from removing the external dependency the nodejs-github-bot is in
practise, it also reduces the bar for contributors since the resulting
project is a lot smaller and less complex than nodejs/github-bot.

PR-URL: https://github.com/nodejs/node/pull/38301
Fixes: https://github.com/nodejs/github-bot/issues/294


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>