feat(volo-http): use generic types for resp and err

[yukiiiteru]

Motivation

The previous code uses a fixed Service with Response = ServerResponse and Error = Infallible, which is not flexible enough.

Solution

This PR updates Services for server. Its Response can be of any type with IntoResponse, and Error can be any type without trait. The only restriction is that the Error must be converted to ServerResponse (with Error = Infallible) before it is given to the client.

In other words, you can define your own error code in the business code, but you must handle it before sending it to client.

An example is also updated where you can create a service with an error code (usize in the example, which doesn't implement IntoResponse) and wrap it with a layer to convert it.