Use current subscription

[ghost]

Is your feature request related to a problem? Please describe.
Using this module requires to know the subscriptionID. While it is good to allow choosing a specific subscription, it would be nice to avoid the need for specifying it, when using the current subscription.

Describe the solution you'd like
Make the subscription_id parameter optional and use current subscription of azurerm context.

Describe alternatives you've considered
A problem may be, that we require azurerm provider only to get the current subscription.