[CI/CD] Write Github actions to build precompiled plugins

[BrettCleary]

Write Github actions to automate building and optionally releasing web3.unreal for different engine versions so that a working precompiled plugin is always available and the build steps are transparent and through a trusted third party.

Engine versions that should be supported are 4.27, 5.0, 5.1 although it may not be necessary to build 3 separate times for full compatibility.

[BrettCleary]

use this command to build the plugin Engine\Build\BatchFiles\RunUAT.bat BuildPlugin -Plugin=[Path to .uplugin file, must be outside engine directory] -Package=[Output directory] -Rocket

as mentioned on https://www.unrealengine.com/en-US/marketplace-guidelines#263b