Extract usage of internal API from TestClustersPlugin and PluginBuildPlugin and related plugins and build logic
This includes a refactoring of ElasticsearchDistribution to handle types
better in a way we can differentiate between supported Elasticsearch
Distribution types supported in TestCkustersPlugin and types only supported
in internal plugins.
It also introduces a set of internal versions of public plugins.
As part of this we also generate the plugin descriptors now.
As a follow up on this we can actually move these public used classes into
an extra project (declared as included build)
We keep LoggedExec and VersionProperties effectively public And workaround for RestTestBase
e609e07cfe