[feature] specify subscription through config.json?

[ltalirz]

Is your feature request related to a problem? Please describe.
This is just a minor suggestion but it appears that azhpc uses the user's default subscription, which means the user needs to be careful to always set it to the correct one before using the tool.

Describe the solution you'd like
I notice that in the newer az-hop, the subscription to use is part of the config.yml.
This seems safer and might be worth adding to azhpc's config.json as well.