Add ability to deserialize other Content-Types

[conniey]

Currently, if the Content-Type is not application/xml, it will assume the Content-Type is JSON. The Service Bus APIs return "application/atom+xml", which is being incorrectly deserialized as JSON.

SerializerEncoding: https://azuresdkdocs.blob.core.windows.net/$web/java/azure-core/1.3.0-beta.1/com/azure/core/util/serializer/SerializerEncoding.html#fromHeaders-com.azure.core.http.HttpHeaders-

It would be nice to add a way to associate other content types with serializers and treat the HTTP requests and responses according to which ones can be handled.

[alzimmermsft]

This problem should be resolvable by enhancing the Content-Type to SerializerEncoding mapping. Instead of checking static values we should be a little be more flexible by parsing the Content-Type header. application/atom+xml is using the suffix definition defined in RFC 3023, and this should work for other suffix types that we see in AppConfig and other services.

[alzimmermsft]

Should be resolved by #11255