Extended parameter attributes for handlers & generic [Entity] attribute

[jeremydmiller]

The HTTP support has this:

/// <summary>
///     Base class for attributes that configure how an HTTP endpoint on a parameter is handled by applying
///     middleware or error handling rules
/// </summary>
[AttributeUsage(AttributeTargets.Parameter)]
public abstract class HttpChainParameterAttribute : Attribute
{
    /// <summary>
    ///     Called by Wolverine during bootstrapping to modify the code generation
    /// for an HTTP endpoint with the decorated parameter
    /// </summary>
    /// <param name="chain"></param>
    /// <param name="parameter"></param>
    /// <param name="container"></param>
    public abstract Variable Modify(HttpChain chain, ParameterInfo parameter,
        IServiceContainer container);
}

Which is used for the [Document] and [Aggregate] attributes in the Marten integration. Good stuff IMO. But there's nothing for that in the message handlers, and nothing like that for the EF Core or RavenDb support.

What if we had something more generic Wolverine core for message handlers that could also be helpful to HttpChains as well? And extend the IPersistenceFrameProvider abstraction to help generate code for a more generic [Entity] attribute?

There's another wrinkle. The existing [Document] attribute for Marten HTTP integration has the concept of being Required, and will return a 404 if not found. Maybe the HandlerChain / HttpChain model has some concept of "early exit" so that the same basic code can be used in both places, but let the chain alter based on whether or not it's HTTP or a message chain.