Grist: settings and documentation for debugging step by step

[fflorent]

As a developer, I had to find out how to debug step by step Grist when working with multiple workers.

I found some tweaks to achieve that (disable liveness probes, activating port forwarding, tweak the NODE_OPTIONS env variable, etc.), but maybe this could be made easy with:

• where applicable, some configuration / scripts to make the setup as smooth as possible (see [Grist] tweak the values for allowing debugging containers #22);
• if possible, make a script that enable port forwarding;
• and documentation for the rest;