Add automatic OpenAPI schema generation via Django

[rush42]

This PR introduces swagger-ui/openapi documentation for the /fahrradparken API-endpoints.

[codecov[bot]]

Codecov Report

Merging #686 (e12481e) into develop (80ef2b5) will decrease coverage by 0.12%. The diff coverage is 50.00%.

@@             Coverage Diff             @@
##           develop     #686      +/-   ##
===========================================
- Coverage    86.18%   86.06%   -0.13%     
===========================================
  Files          219      219              
  Lines         5365     5383      +18     
===========================================
+ Hits          4624     4633       +9     
- Misses         741      750       +9     

Impacted Files	Coverage Δ
fahrradparken/urls.py	55.00% <40.00%> (-45.00%)	:arrow_down:
fahrradparken/views.py	87.07% <100.00%> (+0.26%)	:arrow_up:

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[rush42]

Update:

• generating the schema works properly but still raises warnings on duplicated operationIds
• further customization to the schema is configured through thegenerator_class argument in the get_schema_view method (filtering for 'GET' methods)

[rush42]

I reverted all of the above changes in fixmyapp, as our current goal is only to document the endpoints in /api/fahrradparken

[ohrie]

You can merge this, if you want.