Add new DateTime format - yyyy-MM-dd'T'HH:mm:ss.ffffffK (#422)

Fix #421 

See "O" or "o" in
https://learn.microsoft.com/en-us/dotnet/standard/base-types/standard-date-and-time-format-strings

Co-authored-by: Your Name <you@example.com>

src/Elastic.CommonSchema/PropDispatch.cs

@@ -169,7 +169,8 @@ private static bool TrySetDateTimeOffset(object value, out DateTimeOffset d)
 				var formats = new[]
 				{
 					"yyyy-MM-ddTHH:mm:ss.FFFK",
-					"yyyy-MM-dd'T'HH:mm:ss.FFFK"
+					"yyyy-MM-dd'T'HH:mm:ss.FFFK",
+					"yyyy-MM-dd'T'HH:mm:ss.ffffffK"
 				};
 				d = DateTimeOffset.ParseExact(s, formats, CultureInfo.InvariantCulture, DateTimeStyles.None);
 				return true;