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/execution_command_shell_started_by_svchost.toml

@@ -13,6 +13,10 @@ index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
 language = "eql"
 license = "Elastic License v2"
 name = "Svchost spawning Cmd"
+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 = 21
 rule_id = "fd7a6052-58fa-4397-93c3-4795249ccfa2"
 severity = "low"
@@ -39,11 +43,12 @@ process where event.type == "start" and
 framework = "MITRE ATT&CK"
 [[rule.threat.technique]]
 id = "T1059"
-reference = "https://attack.mitre.org/techniques/T1059/"
 name = "Command and Scripting Interpreter"
+reference = "https://attack.mitre.org/techniques/T1059/"
 
 
 [rule.threat.tactic]
 id = "TA0002"
-reference = "https://attack.mitre.org/tactics/TA0002/"
 name = "Execution"
+reference = "https://attack.mitre.org/tactics/TA0002/"
+