Allow processing of additional_context envelopes when using Flow Registry
Problem to solve
Previous Flows allows for passing in additional context and unfolding those paramters via the CONTEXT_REGISTRY
Proposal
Add similar functionality to the flow registry. Ideally patching it will tie it up with some levels of validation, we could consider extending flow section of flow config to declare how additional context envelopes should look like.
A first implementation could just specify which fields are allowed and required in the additional context.