[Feature] Custom Provider choices available on the reference.json

[hjoaquim]

1. Why? (1-3 sentences or a bullet point list):

   • make that custom provider choices available in the reference, enables other clients to leverage it for their own purpose

2. What? (1-3 sentences or a bullet point list):

   • change package builder and argparse translator to account for custom choices defined on the provider level

3. Impact (1-2 sentences or a bullet point list):

   • Minor UX improvement on the CLI

4. Testing Done:

   • Check for autocompletion on the CLI, example: economy/calendar --country ...