Expand timestamp override tests (#1907)

* Expand timestamp_override tests
* removed timestamp_override from eql sequence rules
* add config entry for eql rules with beats index and t_o
* add timestamp_override to missing fields

rules/windows/persistence_startup_folder_scripts.toml

@@ -1,7 +1,7 @@
 [metadata]
 creation_date = "2020/11/18"
 maturity = "production"
-updated_date = "2021/03/03"
+updated_date = "2022/03/31"
 
 [rule]
 author = ["Elastic"]
@@ -11,6 +11,10 @@ index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
 language = "eql"
 license = "Elastic License v2"
 name = "Persistent Scripts in the Startup Directory"
+note = """## Config
+
+If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.
+"""
 risk_score = 47
 rule_id = "f7c4dc5a-a58d-491d-9f14-9b66507121c0"
 severity = "medium"