feat: implement the docker client package

[Tpuljak]

Docker Client Package

Description

This PR contributes the docker pkg that holds the DockerClient interface and implementation. The DockerClient is meant to be reused in all "Docker-based" providers (e.g. Docker, Digital Ocean, etc.).
This will make the code much more maintainable in those providers.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings