[BugFix] Fix Coverage Router

[deeleeramone]

1. Why?:

   • /coverage/command_model creates a KeyError
   • Fixing the KeyError creates a new problem, the output cannot be serialized.

2. What?:

   • Add logic to parse the nested objects and serialize the output.
   • Includes coverage in the API when OpenBB router extensions are installed with routes.

3. Impact:

   • OPENBB_DEV_MODE environment variable does does not need to be set to include this reference data.
   • Provides the API with model mappings that are more ready-to-use and easier to navigate.

4. Testing Done:

   • OPENBB_DEV_MODE environment variable doesn't need to be set now.
   • Using the /coverage/command_model from the API no longer breaks.