Use a context for storing the environment config

[hguerrero]

Use a config file to store the information regarding PROVIDER_KEY, PROVIDER_DOMAIN information, and add the command like config, set context, and current-context

[rmgrimm]

Ideally, the tool would remain usable without additional files on the filesystem. This facilitates use with containers (both in a Tekton pipeline, as a podman/docker run, etc) without needing to mount a config file into the container every run.

In order to simplify working with various different 3scale tools, I'm planning to allow 3scale-cms to read 3scalerc.yml files in the format of 3scale-toolbox. Then this cms tool could also follow the pattern of 3scale-toolbox in allowing the remote server to still be specified on the command-line as an option.

[hguerrero]

Using a config file in the toolbox style or another makes it easier for people to use the interactive mode. I think for docker and container, even looking for the env variables THREESCALE_PROVIDER_DOMAIN and THREESCALE_ACCESS_TOKEN should be the default if no options are provided.

The order of usage would be:

1. config file
2. env variables
3. command options