Add node container support

[mackensen]

This adds a node container, locked at the necessary core-supported version, for running grunt tasks. The script is based on a Stackoverflow post: https://stackoverflow.com/a/37102013. It's a work-around to ensure that the Moodle web root is loaded before the container runs the command. The expected result (verified locally) is that grunt watch is running and compiling changes. There's probably a more elegant solution to this but I wanted to share what I'd gotten working.

[septatrix]

Why not use FROM node? Also there is already a discussion about including node in the moodle-apache-php image

[odeialba]

Suggested change

	FROM debian:stretch-slim
	FROM node

[odeialba]

Suggested change

	- "${MOODLE_DOCKER_WWWROOT}:/var/www/html
	- "${MOODLE_DOCKER_WWWROOT}:/var/www/html"

[odeialba]

Suggested change

	RUN curl -sL https://deb.nodesource.com/setup_8.x | bash -
	RUN curl -sL https://deb.nodesource.com/setup_14.x | bash -

[odeialba]

Suggested change

	ADD ./bin/start-grunt.sh .
	ADD ./bin/start-grunt.sh .
	USER root
	RUN chmod 755 ./start-grunt.sh

[stronk7]

Hi,

as far as we include .nvmrc for all currently supported versions of Moodle (and older), wouldn't be better to include in the webserver image also nvm, so a simple nvm install & nvm use does the trick within the webserver container?

The problem I can see with this PR is that it requires us to be sticky to a given node version and that can be tricky.

Note I've not tried the idea above, maybe it has other problems, just I'm not sure if adding any extra node container really helps, hence, thinking about potential alternatives.

Also, side note: since #242 is possible to have a new local.yml file providing as many customisations as wanted. This may fall under those customisations easily, I imagine.

Thoughts about the idea (or any other idea related to ease of node/npm use) ?

Ciao :-)