Add GitHub Actions Workflow and update Dockerfile to build

[duhow]

This will build a Container image and publish to ghcr.io (this GitHub repository).

Dockerfile is modified to be self-contanied (so it can build anywhere), but it requires having TechnitiumSoftware/TechnitiumLibrary present in the same folder.

[ShreyasZare]

Thanks for the PR. However, I cannot accept it since it breaks my existing local build process.

[duhow]

@ShreyasZare would you accept another way of delivering an automated build process, rather than just closing this directly? Any specific request?

[ShreyasZare]

The build process I have setup locally builds everything which includes windows installer, linux installation tar file, and docker image with deployment to docker hub. The docker image already being available on docker hub, I do not wish to have it hosted in another place to keep it simple.