OpenAPI: Filter endpoints based on GenerateControllerEndpoints usage

[bkoelman]

This PR filters the listed JSON:API endpoints in the produced swagger.json.

Auto-generated controllers

When using auto-generated controllers, only the endpoints defined on the resource type are shown. For example:

[Resource(GenerateControllerEndpoints = JsonApiEndpoints.Post | JsonApiEndpoints.Patch)]
public sealed class Person : Identifiable<long>
{
    // ...
}

now only displays the corresponding endpoints:

This means that if you're adding a custom implementation of an action method in your partial class, you need to add its flag on [Resource] for it to become listed. If you don't, the method is assumed to exist solely to throw an exception when used.

This is needed because auto-generated controllers derive from JsonApiController<,>, which contains all JSON:API controller action methods. At runtime, an exception is thrown when the endpoint is not accessible.

Hand-written controllers

When not using auto-generated controllers, all exposed endpoints are listed. To hide some, derive from BaseJsonApiController instead of JsonApiController and include only the action methods that should be exposed by adding attributes like [HttpGet], [HttpPost], etc. There's no way to add action methods that always throw without them being listed.

Closes #1052.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (6c9aff8) 90.68% compared to head (71db1dd) 90.67%.

Files	Patch %	Lines
...ApiDotNetCore.OpenApi/OpenApiEndpointConvention.cs	83.87%	2 Missing and 3 partials ⚠️
...JsonApiMetadata/JsonApiEndpointMetadataProvider.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           openapi    #1450      +/-   ##
===========================================
- Coverage    90.68%   90.67%   -0.02%     
===========================================
  Files          390      390              
  Lines        12717    12735      +18     
  Branches      2056     2061       +5     
===========================================
+ Hits         11532    11547      +15     
- Misses         771      772       +1     
- Partials       414      416       +2     

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