[DOCS] Add random default datafeed query delay
Original commit: elastic/x-pack-elasticsearch@36dafe01e4d0dbb00b5f5fcc8d0cce21f3d380f9
@@ -41,7 +41,9 @@ A {dfeed} resource has the following properties:
`query_delay`::
(time units) The number of seconds behind real time that data is queried. For
example, if data from 10:04 a.m. might not be searchable in {es} until
- 10:06 a.m., set this property to 120 seconds. The default value is `60s`.
+ 10:06 a.m., set this property to 120 seconds. The default value is randomly
+ selected between `60s` and `120s`. This randomness improves the query
+ performance when there are multiple jobs running on the same node.
`script_fields`::
(object) Specifies scripts that evaluate custom expressions and returns
