Producer must respect ReadCommitted isolation

[sehz]

We need to support following isolation level for producer

• ReadUncommitted - Just wait for leader to write message (only wait for LEO update)
• ReadCommitted - Wait for messages to be committed (wait for HW)

This was implemented in previous version of Fluvio but somehow it got lost. The isolation level must be exposed in the Producer Config.

[galibey]

This is the current state of this feature:

• Isolation is the property of the Consumer. Specified in ConsumerConfig. It is used by the Stream handler and defines when records should be sent back to the consumer.
• As stated in the description:
  ReadUncommitted - Just wait for leader to write message (only wait for LEO update)
  ReadCommitted - Wait for messages to be committed (wait for HW)
• fluvio-cli doesn't support specifying the isolation, only Rust API client does.

I did local testing with 3 spu and depending on isolation the latency of read/write operation differs significantly indicating that the feature works. Do we need some deep verification of the isolation guarantees?

[sehz]

Yes. We should allow CLI to specify isolation level for Consumer and producer.