AuthorizeRequestValidator returns unsupported_response_type when no response_type is supplied

[user1336]

Which version of Duende IdentityServer are you using?
Latest (6.3.5)

Which version of .NET are you using?
.NET 7

Describe the bug
If there is no response_type specified on the Authorize endpoint we return an unsupported_response_type.

RFC 6749 section 4.2.1 specifies that response_type is a required parameter:

response_type REQUIRED. Value MUST be set to "token".

RFC 6749 section 4.1.2.1 also specifies:

invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed.
and
unsupported_response_type The authorization server does not support obtaining an authorization code using this method.

Since response_type is a required parameter we are of the opinion that actual error, when this field is absent, should be invalid_request instead of unsupported_response_type.

Expected behavior
The AuthorizeRequestValidator should return a different Invalid(...) response specified on this line.

Additional context
Simular issue to #44

[AndersAbel]

Thank you for reporting and for your PR. We will track and comment this issue in the pull request so I am closing this issue.