ESQL - add some CSV tests for current timezone behavior (elastic#127181) (elastic#127233)

I just needed to check the current behavior around this, and figured I'd add the queries I used as CSV tests for future reference.

Author: not-napoleon

x-pack/plugin/esql/qa/testFixtures/src/main/resources/date.csv-spec

@@ -200,6 +200,30 @@ birth_date:date         |bd:date
 1964-06-02T00:00:00.000Z|1964-06-02T00:00:00.000Z
 ;
 
+convert with zones
+ROW str = "2025-04-11T05:00:00+0400"
+| EVAL dt = TO_DATETIME(str);
+
+str:String                 | dt:datetime
+"2025-04-11T05:00:00+0400" | 2025-04-11T01:00:00.000Z
+;
+
+equality with zones
+ROW dt = TO_DATETIME("2025-04-11T01:00:00.000Z")
+| EVAL bool = "2025-04-11T05:00:00+0400" == dt;
+
+dt:datetime              | bool:boolean
+2025-04-11T01:00:00.000Z | true
+;
+
+convert no zone
+ROW str = "2025-04-11T05:00:00.000"
+| EVAL dt = TO_DATETIME(str);
+
+str:String                 | dt:datetime
+"2025-04-11T05:00:00.000" | 2025-04-11T05:00:00.000Z
+;
+
 convertFromString#[skip:-8.13.99, reason: default date formatter is changed in 8.14]
 // tag::to_datetime-str[]
 ROW string = ["1953-09-02T00:00:00.000Z", "1964-06-02T00:00:00.000Z", "1964-06-02 00:00:00"]