Map Wolverine TenantId from incoming MassTransit messages

[outofrange-consulting]

What

Adds a MapTenantIdFrom<T> hook to the MassTransit interop so applications consuming MassTransit messages can populate Wolverine's Envelope.TenantId from each incoming message:

opts.ListenToRabbitQueue("orders")
    .UseMassTransitInterop(mt =>
    {
        // from the strongly-typed message body...
        mt.MapTenantIdFrom<OrderPlaced>(env => env.Message?.TenantId);

        // ...or from MassTransit envelope metadata (headers, addresses, ids)
        mt.MapTenantIdFrom<OrderShipped>(env =>
            env.Headers.TryGetValue("tenant-id", out var v) ? v?.ToString() : null);
    });

The lambda receives a new public read-only view, IMassTransitEnvelope<T>, exposing the deserialized Message alongside the surrounding MassTransit metadata. The concrete MassTransitEnvelope<T> stays internal, so the mutable serialization DTO is not leaked onto the public surface.

Behavior:

• Multiple message types compose — each mapper only fires for its own T (re-registering the same T replaces the prior mapping).
• A null/empty result never overwrites an existing TenantId.
• Inbound (deserialization) path only.

Drive-by fix

While wiring this up I found that UseMassTransitInterop(configure) dropped the configure lambda on the Rabbit MQ and Amazon SQS listeners: Rabbit MQ called InteropWithMassTransit() with no argument, and the SQS MassTransitMapper never received it. As a result any serializer customization — including the existing UseSystemTextJsonForSerialization, and now MapTenantIdFrom — silently no-opped on those transports while only Azure Service Bus honored it. This is threaded through on both, in its own commit so it can be reviewed (or split) independently.

Tests (no broker required)

• MassTransitTenantMappingTests (CoreTests) — body mapping, header mapping, unregistered-type pass-through, empty-no-overwrite, multi-type dispatch, full-chain fall-through.
• masstransit_interop_map_tenant_id (RabbitMQ.Tests) — drives the full deserialization pipeline with a real MassTransit wire payload through TryDeserializeEnvelope, proving the configure lambda reaches the listener. Uses stubbed transports.
• masstransit_mapper_tenant_mapping (AmazonSqs.Tests) — confirms the SQS mapper applies the configure lambda.

Docs updated under docs/guide/messaging/transports/rabbitmq/interoperability.md. dotnet build wolverine.slnx -c Release is clean locally.

[jeremydmiller]

Thanks @outofrange-consulting! Superseded by #3192, which retains your original commits (and authorship) and adds a small public-API rework on top: rather than introducing a new IMassTransitEnvelope<T> interface, it exposes the concrete MassTransitEnvelope/MassTransitEnvelope<T> type publicly and removes the interface, so MapTenantIdFrom<T> takes Func<MassTransitEnvelope<T>, string?>.

Closing in favor of #3192 — please follow along there. 🙏