Update Documentation for Message Object Instantiation (#2135)

* update documentation for msg object instantiation with warning

* add warning block as suggested

* fix whitespace

* fix code formatting

Author: ojasvajain

src/confluent_kafka/src/confluent_kafka.c

@@ -815,6 +815,34 @@ PyTypeObject MessageType = {
     "object is a proper message (error() returns None) or an "
     "error/event.\n"
     "\n"
+    ".. py:function:: Message([topic], [partition], [offset], [key], [value], "
+    "[headers], [error], [timestamp], [latency], [leader_epoch])\n"
+    "\n"
+    "  Instantiate a Message object.\n"
+    "\n"
+    "  .. warning::"
+    "    This constructor is intended **only for testing and mock scenarios**."
+    "    Do **not** use user instantiated Message object in mainstream APIs or "
+    "in production."
+    "    Using this constructor outside of test environments may result in"
+    "    unexpected behavior, security issues, or inconsistent application "
+    "state.\n"
+    "\n"
+    "  All parameters are optional.\n"
+    "\n"
+    "  :param string topic: Topic name\n"
+    "  :param int partition: Partition number\n"
+    "  :param int offset: Message offset\n"
+    "  :param bytes key: Message key\n"
+    "  :param bytes value: Message value\n"
+    "  :param list headers: Message headers\n"
+    "  :param KafkaError error: KafkaError object\n"
+    "  :param tuple timestamp: (Timestamp type (int), Message epoch timestamp "
+    "in seconds (int))\n"
+    "  :param float latency: Message latency in seconds\n"
+    "  :param int leader_epoch: Message leader epoch in seconds\n"
+    "  :rtype: Message\n"
+    "\n"
     ".. py:function:: len()\n"
     "\n"
     "  :returns: Message value (payload) size in bytes\n"