Support docker in testclusters so we can swap it in any of the existing tests #40732
Description
We identified a problem in #40723 that would have been caught by mixed cluster tests running with docker.
Since neither of the existing issues #37617 nor #38053 would have caught this, we need to go one step beyond and create the ability to swap to the docker distribution in any of the existing tests.
This proposal is to implement support in testcluster to be able to start a test cluster using docker.
This will give us the ability to implement specific ci jobs that test with docker, specific tasks, or randomize the distribution type (zip or docker) when running the tests.