Expose the logic to process Docker Context outside the internal package

[jjbustamante]

Description

With pack 0.31.0 we added support for reading the configuration from the docker context and set the environment variables required by pack accordingly. That logic was added into the internal package which means it can't be reuse by the community who uses pack as library.

Double checking this code, I think it is save if we move it outside the internal package, in that case, end-uses can decide to call the method before creating a pack client if they want.

Currently the way we create a pack client can be checked here

Proposed solution

Move the files: internal/docker/context.go and internal/docker/context_test.go to pkg/client

Describe alternatives you've considered

I thought on moving the context processing method inside the client.NewClient method, in this way it will simplify the pack client creation process.

Additional context

• This feature should be documented somewhere