Use testcontainers-kafka for integration tests

[Z1kkurat]

Motivation: we avoid pulling Kafka broker code into our test scope. This has a few benefits:

• Kafka broker is independent of the Java version used. It's not an issue as far as I currently know, but it might be in the same spirit it was for Cassandra which required additional settings to be run with Java 11+
• we can safely update our dependencies without possibly affecting Kafka broker (as they are in the same classpath currently)
• it models a test case that's closer to a live usage - a separate broker, running in a separate container, rather than in the same JVM
• it opens up a possible path of cross-compiling this library to Scala 3 since Kafka broker code is compiled against a specific Scala version
• we bring fewer dependencies to the test scope, using only those we bring in with kafka-clients library
• there won't be a mismatch between the used kafka-clients and Kafka broker versions. Using a different version is a matter of updating testcontainers-scala-kafka dependency or specifying a different image version manually

[coveralls]

Pull Request Test Coverage Report for Build 5452618040

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 76.731%

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Totals
Change from base Build 5070546918:	0.2%
Covered Lines:	1352
Relevant Lines:	1762

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💛 - Coveralls