Support parsing ISO 8601 datetime format for timestamp value

Signed-off-by: Yuanchun Shen <yuanchu@amazon.com>

Author: yuancu

core/src/main/java/org/opensearch/sql/data/model/ExprTimestampValue.java

@@ -13,6 +13,8 @@
 import java.time.LocalDateTime;
 import java.time.LocalTime;
 import java.time.ZoneOffset;
+import java.time.ZonedDateTime;
+import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
 import java.time.temporal.ChronoUnit;
 import java.util.Objects;
@@ -31,17 +33,24 @@ public class ExprTimestampValue extends AbstractExprValue {
   /**
    * Constructor with timestamp string.
    *
-   * @param timestamp a date or timestamp string (does not accept time string)
+   * @param timestamp a date or timestamp string (does not accept time string). It accepts both ISO
+   *     8601 format and {@code yyyy-MM-dd HH:mm:ss[.SSSSSSSSS]} format
    */
   public ExprTimestampValue(String timestamp) {
     try {
-      this.timestamp =
-          LocalDateTime.parse(timestamp, DateTimeFormatters.DATE_TIMESTAMP_FORMATTER)
-              .toInstant(ZoneOffset.UTC);
+      LocalDateTime ldt;
+      try {
+        ldt = LocalDateTime.parse(timestamp, DateTimeFormatters.DATE_TIMESTAMP_FORMATTER);
+      } catch (DateTimeParseException ignored) {
+        ZonedDateTime zdt = ZonedDateTime.parse(timestamp, DateTimeFormatter.ISO_DATE_TIME);
+        ldt = zdt.withZoneSameInstant(ZoneOffset.UTC).toLocalDateTime();
+      }
+      this.timestamp = ldt.toInstant(ZoneOffset.UTC);
     } catch (DateTimeParseException e) {
       throw new ExpressionEvaluationException(
           String.format(
-              "timestamp:%s in unsupported format, please use 'yyyy-MM-dd HH:mm:ss[.SSSSSSSSS]'",
+              "timestamp:%s in unsupported format, please use 'yyyy-MM-dd HH:mm:ss[.SSSSSSSSS]' or"
+                  + " ISO 8601 format",
               timestamp));
     }
   }