feat(api): add openapi specification

[ReenigneArcher]

Description

This PR will attempt to provide an openapi spec for the Sunshine rest API. I am not an expert on this, but I believe once this is available it will be possible to automatically create SDKs in various languages using an SDK generator (https://openapi.tools/#sdk).

The idea came from https://plexapi.dev/Open-API-Specification which generates SDKs using "Speakeasy". Unfortunately, I don't believe Speakeasy has a generous open source license/option, so other generators may need to be considered. Still, the repo has been a good example, starting with the main spec file - https://github.com/LukeHagar/plex-api-spec/blob/main/src/pms-spec.yaml

Additionally, there are spec generators for various languages, but none seem to be available for c++, understandably, so this is being manually created.

TODO:

• CI, build API docs using redoc, lint, etc. redoc: https://dev.to/heymich/a-guide-to-creating-api-documentation-with-redoc-and-github-pages-4i4a
• see if this even works
  • postman, see: Unable to render a path item extracted into components section Redocly/redoc#2457 (comment)
  • redocly in CLion (not working... probably CORS issue... also same as Unable to render a path item extracted into components section Redocly/redoc#2457 (comment))
  • swagger in CLion (not working... probably CORS issue)
• add all endpoints
• generate version number (and other variables) during build/release
• generate/publish SDKs (possibly in separate repos)
• return properly serialized json (boolean, integer) values (probably not this PR)... then remove "types" directory

Other notes:

• if redoc doesn't work out... standalone linting: https://github.com/stoplightio/spectral
• might be better to use a different web framework: https://github.com/oatpp/oatpp-swagger

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 11.62%. Comparing base (257a102) to head (5b863f7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3540   +/-   ##
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  Coverage   11.62%   11.62%           
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  Files          93       93           
  Lines       17319    17319           
  Branches     8085     8085           
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  Hits         2014     2014           
  Misses      12823    12823           
  Partials     2482     2482           

Flag	Coverage Δ
Linux	11.30% <ø> (ø)
Windows	13.04% <ø> (ø)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud