This change disables the _all meta field by default.
Now that we have the "all-fields" method of query execution, we can save both
indexing time and disk space by disabling it.
_all can no longer be configured for indices created after 6.0.
Relates to #20925 and #21341Resolves#19784
* Allows for an array of index template patterns to be provided to an
index template, and rename the field from 'template' to 'index_pattern'.
Closes#20690
Lee Hinman
Clinton Gormley
Alexander Lin
Adrien Grand