Add minimal docker image to tun pyth-agent

[146karol]

The purpose of the PR is to add minimal docker image to run pyth-agent while keeping it to be able to build the program.

It was achieved using multi stage process:

• first stage "builder" installs dependencies, gets code and perform build itself,
• second stage installs just runtime dependencies.

Image build from the agent.Dockerfile has size 132 MB, while image build from Dockerfile has size around 5.65GB

[jayantk]

thank you @146karol !

[146karol]

@jayantk I added new line at the end of the file. Could you please re-trigger the workflow check?

[jayantk]

thanks again! and appreciate you making CI pass -- i was just about to push a commit to this when i realized you already did it.

[kietng-alpha]

@jayantk Can we add a minimal tag for this? We would love to use this minimal image without rebuilding it.