[Feature] Add Support for Generating AsyncAPI

[iancooper]

Is your feature request related to a problem? Please describe.
Similar to how OpenAPI support works in ASP.NET, it should be possible to generate an AsyncAPI document to represent the brokers, channels, messages, and operations used by the application.

Describe the solution you'd like
Similar to the way AddSwaggerGen(), it should be possible to generate an AsyncAPI document in Brighter via AddAsyncAPIGen(). We would then document the endpoints exposed by the application.

It probably makes sense to use the AsyncAPI .NET https://github.com/asyncapi/net-sdk to produce the AsyncAPI document.

Since we don't automatically set up a website, we won't add one to display AsyncAPI documentation.

We should add protocol-specific bindings that allow configuration, provided we have the necessary information to complete them.

Describe alternatives you've considered
We could go with a contract-first approach and generate the Brighter client from AsyncAPI. However, we will leave that to a separate story about scaffolding.

[PaulOberg1]

Hi @iancooper I would be interested in contributing here. Could I be assigned? 😊

[iancooper]

Go for it. Ask any questions you need. An ADR in the first commit helps us give feedback