Allows ML datafeeds to work with time fields that have
the "date_nanos" type.  (Previously datafeeds only
worked with time fields that had the "date" type.)

Co-Authored-By: David Kyle <david.kyle@elastic.co>

The extractor for the primary time field of an anomaly
detection job is automatically created as a TimeField
without checking its field caps response, so earlier
changes in this PR did enough to make that scenario
work for "date_nanos" fields.  However, the main field
type detection code was still only accepting "date"
to create a TimeField.  This change makes it accept
either or both of "date" and "date_nanos".

…droberts195/elasticsearch into make_datafeed_work_with_nanosecond_time

Profiling showed the low level version is 3 times faster
and we do time parsing for every single document fed to
a job.