ci deb: extract confluent test case

[kenhys]

In the previous versions, testing with confluent is executed in serverspec:linux.

As confluent test case should be out of scope about basic serverspec to distinct confluent's failure, so extract them as isolated test case.

• github ci: added "Confluent Test"
• Upgrade confluent from 6.0 to 7.6
• Replace deprecated --zookeeper option to --bootstrap-server to create kafka topics