Include Apache Harry for fuzzy testing

[grighetto]

┆Issue is synchronized with this Jira Task by Unito
┆Issue Number: AD-70

[grighetto]

Right now, Harry seems to be hardcoded to run against Cassandra's in-JVM dtests. According to the docs, it's supposed to be able to run against an external cluster too, which is what we need for this project.
Thi is the main runner class: https://github.com/apache/cassandra-harry/blob/a8270c786bf75e0c77f084d45f9900c3c111f97f/harry-runner/src/harry/runner/HarryRunner.java.
It calls runWithInJvmDtest right away.

I found https://github.com/apache/cassandra-harry/blob/a8270c786bf75e0c77f084d45f9900c3c111f97f/harry-integration/src/harry/model/sut/ExternalClusterSut.java, but it's not referenced anywhere else in the codebase.

We should probably make it more flexible and allow for defining an external cluster in the config.yaml.