Make the field_stats behavior for expanding indices not default for new index patterns

[epixa]

With the completion of elastic/elasticsearch#23946, Elasticsearch should now support querying directly on wildcard indices without having to jump through hoops using field_stats to expand the calls out to multiple requests to specific indices.

In anticipation of deprecating and removing the field_stats feature entirely, we should update the management screen for index patterns to make the field_stats behavior opt-in rather than the default.

Before:

After: