Add default_field option to fields.yml (elastic#14341)

* Add default_field option to fields.yml

The number of fields in the Elasticsearch index template's `settings.index.query.default_field` option has grown over time, and is now greater than 1024 in Filebeat (Elastic licensed version). This causes queries to Elasticsearch to fail when a list of fields is not specified because there is a default limit of 1024 in Elasticsearch.

This adds a new setting to fields.yml called `default_field` whose value can be true/false (defaults to true). When true the text/keyword fields are added to the `default_field` list (as was the behavior before this change). And when set to false the field is omitted from the default_field list.

This adds a test for every beat to check if the default_field list contains more than 1000 fields. The limit is a little less than 1024 because `fields.*` is in the default_field list already and at query time that wildcard will be expanded and count toward the limit.

Fixes elastic#14262

* Exclude new zeek datasets from default_field list

(cherry picked from commit 9f21b96)