Avoid sanitizing the query for query_string searches

[jpeach]

When you do a query_string search, the value is marshaled using sanitizeElasticQueryField, but in this case that probably doesn't do what the caller wants. For example, if the value is "service:foo", the ":" should not be escaped because it need to be parsed as a field delimiter. Probably in this case, you want to pass the value through without any modifications.

https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-query-string-query.html#query-string-syntax