Add support for global error handling

[baywet]

Currently the http core implementations do no try to parse error responses. Those could contain useful information to convey to the consumer.
You can already define responses in open API for HTTP status codes that correspond to errors (4XX, 5XX), however defining those for each endpoint in Microsoft Graph would be fastidious.
Instead we should make use of another feature in openAPI called overlays. This feature is not yet implemented in the openAPI.net lib but it'd allow defining global responses that apply to all the endpoints if not already defined locally.

• get the schema that's defined in overlays
• use that information for the API client (to register the error type)
• modify http core to call deserialization on error response bodies with that type and throw
  AB#10401

[darrelmiller]

Kiota wouldn't need to process the Overlay directly. That overlay code would be implemented somewhere else.

[baywet]

how would the HTTP library know which type to deserialize the error to then?

[darrelmiller]

The Overlay would be processed before Kiota started processing the OpenAPI.

[baywet]

So kiota would see responses with schemas on different response codes. But how would it map the successful response codes with a specific bad response code schéma? Especially if the schema for 5xx differs from 4xx for some reason?

[darrelmiller]

defining those for each endpoint in Microsoft Graph would be fastidious.
Microsoft Graph is fine because we autogen the OpenAPI

For people writing OpenAPI by hand, this feels like an OpenAPI problem, not a Kiota problem. I feel like we should close this issue as this is not where this problem should be solved.