[DOCS] Warn about searching across all fields wt. `query_string` (#55853)
[DOCS] Warn about searching across all fields wt. `query_string` (#55853)

Warn about potential performance impact when a large number of fields
is used with query string query and no default field.

Re-adds content from #35570.
That content was erroneously removed in #45296.

Co-authored-by: Peter Dyson <805b4d2a0a3caa3b24ec0175f23edd96d732f0ed@geekpete.com>
GlenRSmith/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,uschindler/elasticsearch,nknize/elasticsearch