[Rust/Cloudevents] JobSink Integration / Long Running Functions

[pierDipi]

As described in #2586, we need to integrate the Rust CloudEvents functions with JobSink

• when the env variable K_EXECUTION_MODE is equal to batch the runtime will read the event from the file and pass it to the handler
• If the function returns a new event it would be produced to an endpoint that is pointed by K_SINK env variable (if present) (so that you can use JobSink in combination with SinkBinding to have "job callbacks")

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