[mdatagen] Validate context propagation on processors and connectors

[mx-psi]

trafficstars

Component(s)

cmd/mdatagen

Describe the issue you're reporting

Most processors and connectors should propagate context. Since we completed #13039, we can easily test for this by introducing a key with a random value in the context and checking that the key-value pair is recoverable by the next consumer.

We should test this for all signals/signal type combinations. We should have a mechanism to opt out of this autogenerated tests if the component in question does not propagate context