Move existing integration to JADNC

[maurei]

Closes #1048

In the effort of migrating the existing integration that lived in the private repository:

• Moved all of the code from the existing integration to JsonApiDotNetCore.OpenApi
• Introduced the JsonApiDotNetCore.OpenApi.Client project, which currently only introduces support for partial write requests for c# clients generated with NSwag.
• Added a client library test suite to OpenApiTests.
• Introduced the JsonApiDotNetCoreExampleClient project that generates a client for the example project based off the OpenAPI specification that was created using the OpenAPI integration in the example project.
• Updated docs about the usage of a generated OpenAPI client.

Closes #1049

• A matter of replacing ResourceNameFormatterProxy with ResourceNameFormatter.

Closes #1050

• In Introduce a dedicated IApiRequestFormatMetadataProvider, removing the input formatter workaround #1050 it was suggested to reconsider merging changes in Implement API format metadata provider interfaces #972, but it turns out this was never going to work for the OpenAPI integration because it provide metadata about types like for example ResourceCollectionResponseDocument<TResource>, which lives in the OpenAPI integration project and hence cannot be referenced in the main solution. The solution is to just introduce a dedicated formatter with the sole purpose of implementing IApiRequestFormatMetadataProvider, which does not interfere with the regular JsonApiInputFormatter, and which is only registered when the OpenAPI package is added to the JsonApiDotNetCore application.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• Documentation updated

[codecov]

Codecov Report

Merging #1076 (d3ebfaf) into openapi (d226a0e) will increase coverage by 0.40%.
The diff coverage is 92.46%.

@@             Coverage Diff             @@
##           openapi    #1076      +/-   ##
===========================================
+ Coverage    88.42%   88.82%   +0.40%     
===========================================
  Files          258      306      +48     
  Lines         7039     8057    +1018     
===========================================
+ Hits          6224     7157     +933     
- Misses         815      900      +85     

Impacted Files	Coverage Δ
...jects/Documents/PrimaryResourceResponseDocument.cs	0.00% <0.00%> (ø)
...ts/Documents/ResourceCollectionResponseDocument.cs	0.00% <0.00%> (ø)
...ts/ResourceIdentifierCollectionResponseDocument.cs	0.00% <0.00%> (ø)
...ts/Documents/ResourceIdentifierResponseDocument.cs	0.00% <0.00%> (ø)
...cts/Documents/SecondaryResourceResponseDocument.cs	0.00% <0.00%> (ø)
...DotNetCore.OpenApi/JsonApiObjects/JsonapiObject.cs	0.00% <0.00%> (ø)
.../JsonApiObjects/Links/LinksInRelationshipObject.cs	0.00% <0.00%> (ø)
...Objects/Links/LinksInResourceCollectionDocument.cs	0.00% <0.00%> (ø)
...pi/JsonApiObjects/Links/LinksInResourceDocument.cs	0.00% <0.00%> (ø)
...nks/LinksInResourceIdentifierCollectionDocument.cs	0.00% <0.00%> (ø)
... and 89 more

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[bart-degreed]

Looked at the docs so far, will review more another day.

[bart-degreed]

Done with review pass. Please don't force-push anymore after the code review has started.

[bart-degreed]

Done with another review pass. Still pending:

• review tests, based on the doc you sent me
• update install steps in .md
• diff the swagger.json against internal prototype

[bart-degreed]

Reviewed client tests

[bart-degreed]

Gone over client tests again. Looks good now, except what's listed. Pending: swagger.json