When a transform has a `retention_policy` it needs to be able to delete documents in the destination index.
`create_index` does not necessitate that we can delete documents from it. So, even if we create the index, we need to verify that we can delete documents given the `retention_policy` definition.
This is not a crucial bug as the transform will simply fail later. Its nicer to fail sooner.
closes https://github.com/elastic/elasticsearch/issues/85409
Removes `testenv` annotations and related code. These annotations originally let you skip x-pack snippet tests in the docs. However, that's no longer possible.
Relates to #79309, #31619
