OpenAPI: Fix "id" parameter in URL to be string

[bkoelman]

This PR corrects the "id" parameter type to be string in the JSON:API request URL.

Contributes to #1051:

Also address the following: When using Identifiable where TId is other than string, eg int, the generated client will have its id parameter typed as int in methods, which is incorrect: it should always be string.

QUALITY CHECKLIST

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

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (fda2b36) 91.09% compared to head (b0fa688) 91.08%.

Files	Patch %	Lines
...penApi/SwaggerComponents/JsonApiSchemaGenerator.cs	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           openapi    #1438      +/-   ##
===========================================
- Coverage    91.09%   91.08%   -0.02%     
===========================================
  Files          384      384              
  Lines        12357    12358       +1     
  Branches      1987     1989       +2     
===========================================
- Hits         11257    11256       -1     
  Misses         710      710              
- Partials       390      392       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.