It was previously required that the _start API caller required the same roles as the create API caller.
This does not make sense as when the transform is actually running (after _start) we rely solely on the roles of the caller who created the transform.
Consequently, this commit does the permission validations and various checks with the roles of user who created the transform, not the one calling _start
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
