Allow the Kafka buffer (and others that do not require the heap) to bypass the heap circuit breaker

[dlvenable]

Is your feature request related to a problem? Please describe.

The kafka buffer is currently subject to the heap circuit breaker on receipt of data. Since this buffer writes directly to a Kafka topic, and thus leaves the JVM heap, it shouldn't have the heap circuit-breaker impact it.

Describe the solution you'd like

Provide a new function on Buffer to indicate if the buffer uses off-heap data.

boolean isWrittenOffHeapOnly()

When this is true, then do not apply the CircuitBreaker. This initial logic may not be ideal long-term as we could possibly support other types of circuit-breakers (say based on local disk-space, a CPU-based threshold, or the current pipeline latency). However, this will work for an initial implementation.

Additional context

The kafka buffer already uses the circuit-breaker when reading from the topic to place into the processor chains - #3578.