add 'data.stream.namespace' configuration property

[fbaligand]

Problem

Currently, we cannot fully customize the target data stream.
More precisely, the namespace part of the data stream is necessarily the topic.
This is especially a problem, when you want that a connector consumes several topics for only one target data stream.
More simply, I want to be able to define target data stream name, regardless of the input topic name.

Solution

This PR aims to add a new configuration property named 'data.stream.namespace'.
This property aims to customize data stream "namespace" part (as its name says).
This is an optional setting, that have ${topic} as default value ; so that, by default, it works as currently, no breaking change.
By the way, user is able to define a custom namespace that contains topic name like that:
my_prefix_${topic}

Does this solution apply anywhere else?

• yes
• [x ] no

If yes, where?

Test Strategy

Testing done:

• [ x] Unit tests
• Integration tests
• System tests
• Manual tests

Release Plan

I guess that you (Confluent Inc.) is responsible for release plan.

I am merging to master

It is safe to revert or rollback

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