Ease installation process by uploading pre-built docker images to registries

[TheZ3ro]

Is your feature request related to a problem? Please describe.
Right now, to install pwndoc you need to download the repository and build all the docker images in order to start the containers.
In a modern deployment, Pwndoc images should be pre-built and uploaded inside docker registry (like the dockerhub one, or github itself via actions).
In this way installation is only a matter of downloading the pre-built image instead of re-building the images for every version.

Describe the solution you'd like
Create a Github workflow/action that build pwndoc images and uploads them on a registry.

Additional context
https://github.blog/2020-09-01-introducing-github-container-registry/
https://docs.github.com/en/actions/publishing-packages/publishing-docker-images

[CarlesLlobet]

+1 ❤️