[STUB] Move output middeware to policies behind Outbox

[timolegros]

Description

We should create policies that handle events from the Outbox for each output middleware. This has numerous benefits:

• decouples output middleware logic from commands/queries and routes in general
• enables guaranteed at least once execution of output middleware logic
• improves the performance of the main API process since policy handling can execute outside of the API process

Additional context

[raykyri]

Commenting to subscribe - we can either make a new issue to do the Canvas output middleware after analytics output middleware, or I can work off this one, once analytics output middleware has been migrated over to use the Outbox.