Feature/openapi spec generation improvements 2

[nathanloyer]

My team needs to add custom extensions to the generated openapi spec, so I've put together some changes that will allow us to override the OpenApiInterceptor and customize what gets generated. We're also going to be using this to append more detailed json schema definitions into the spec so developers can quickly see what the FHIR objects look like without jumping out to read the FHIR Docs.

Let me know what you think and if I need to make any adjustments before we can merge. I have been mostly testing with direct integration with my server so far, but I will add more rigorous testing if you agree that this is a useful feature that we can merge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.50%. Comparing base (406db33) to head (f47b27a).
Report is 180 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6651      +/-   ##
============================================
- Coverage     83.54%   83.50%   -0.05%     
- Complexity    27432    28572    +1140     
============================================
  Files          1707     1797      +90     
  Lines        106185   111219    +5034     
  Branches      13397    13971     +574     
============================================
+ Hits          88710    92871    +4161     
- Misses        11750    12359     +609     
- Partials       5725     5989     +264     

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