Object fields cannot be used as features. At the moment _explain
API includes them and even worse it allows it does not error when
an object field is excluded. This creates the expectation to the
user that all children fields will also be excluded while it's not
the case.
This commit omits object fields from the _explain API and also
adds an error if an object field is included or excluded.
This commit replaces the _estimate_memory_usage API with
a new API, the _explain API.
The API consolidates information that is useful before
creating a data frame analytics job.
It includes:
- memory estimation
- field selection explanation
Memory estimation is moved here from what was previously
calculated in the _estimate_memory_usage API.
Field selection is a new feature that explains to the user
whether each available field was selected to be included or
not in the analysis. In the case it was not included, it also
explains the reason why.
