Optimized build and output image

[Radiergummi]

Hey there, a while ago I forked libpostal-rest-docker to make some improvements, and while I plan on keeping our customised image, I wanted to contribute some of those improvements back.

So this PR contains the following changes:

• GitHub action to automatically build and push the image to Docker Hub
• Split in builder and runtime image as multi-stage build (smaller image size)
• Configurable versions of libpostal and libpostal-rest via build args
• Configuration for libpostal-rest via build args/environment variables
• libpostal-rest runs directly instead of a sub-shell, enabling fast shutdowns
• Everything contained in a single Docker image

[Radiergummi]

(I'd recommend not merging this due to the GitHub action pushing my image, but just take it as an inspiration and pick what you need :) )

[johnlonganecker]

I will take a look in the future for sure! thanks @Radiergummi I really appreciate this!

[igrayson]

This would be really great!