Resolve #800. Add Dockerfile and compilation instructions

[PaulZC]

This PR:

• Includes a fix for Firmware 4.3 - Bug in PVT / UDP Server IP display (displayMessageFont) #800
• Adds the Dockerfile and instructions on how to compile the firmware using a stand-alone Docker Image and Container
  • There is now no need to: install the Arduino CLI, the correct ESP32 core, all the required libraries (at the correct version), update form.h for the web config
  • The Dockerfile does it all for you...!

[nseidle]

This is great! Is there a way to have the action run the docker file? This would force us to have a single compilation path. Otherwise, we have to remember to update library versions across multiple files.

[PaulZC]

@nseidle Yeah... I thought you might say something like that! I'm still finding my feet with Docker and Dockerfiles, but, yes, it should be possible... Leave it with me.

I'm making the same changes on the RTK Everywhere Repo. The Dockerfile is working nicely there too.

When you have time, try running it locally on your desktop. The compilation is really quick. They've got some nice optimizations going on in there...