Add a guide for using Composer Patches

[roborourke]

In some instances clients or project teams might be a bit hamstrung waiting for core development to catch up to requirements or there might be some edge case they need to deal with at short notice.

While we're generally pretty good at getting things patched quickly some things are more fundamental like changes to the docker-composer.yml in Local Server.

It would be really handy to provide a guide on the ultimate escape hatch which is using composer to apply patches to packages on install.

We should probably recommend the most complete composer plugin for this out there that I've seen which is https://github.com/vaimo/composer-patches

It covers pretty much all the bases you'd need and has great options for setting version constraints on patches being applied so they can be added with forward compat in mind as well.

The guide should contain:

• how to install the composer plugin eg. composer require
• a couple of complete examples of the composer.json config
• caveats and warnings eg. this is a last ditch resort and we do not support patched modules / deps