Clarify ISO 8601 datetime format in schema

Updated the description for the 'datetime' field to specify that any valid ISO 8601 datetime string is accepted, including local time, UTC, or specific timezones. This provides clearer guidance on acceptable datetime formats.

Author: Rafnuss

measurements-table-schema.json

@@ -41,7 +41,7 @@
     },
     {
       "name": "datetime",
-      "description": "Date and time of the measurement. Formatted as an ISO 8601 string with timezone designator `YYYY-MM-DDThh:mm:ssZ`.",
+      "description": "Date and time of the measurement. Accepts any valid [ISO 8601](https://wikipedia.org/wiki/ISO_8601) datetime string, including datetime in local time (`YYYY-MM-DDThh:mm`), in UTC (`YYYY-MM-DDThh:mmZ`) or any specific timezone (`YYYY-MM-DDThh:mm+hh:mm`).",
       "type": "datetime",
       "constraints": {
         "required": true