Generate bundle interface from dependency usage

[carolynvs]

Dependencies can declare a specific interface, such as the mysql dependency must generate an output containing a mysql connection string. But there is also an interred base interface determined by how the dependency is used by the parent. Porter needs to be able to generate the base interface by determining if the parent bundle uses any outputs, credentials and parameters from the dependency and including those in the base interface.

The templates used in the dependencies (and TBD on the action section, see getporter/proposals#18) must be evaluated and the variables used to see which params/creds/outputs are used.

ℹ️ Read PEP003 - Advanced Dependencies for context about how dependencies should work, design details, and notes about desired behavior.