fix kafka: wait for metadata

Kafka's instance metadata could be unavailable (because it's being filled asynchronously). extract_send_partition() is based on a metadata, so it may return `None` for partition and later cause all type of warning messages (e.g. `Invalid type NoneType for attribute value. Expected one of ['bool', 'str', 'bytes', 'int', 'float'] or a sequence of those types`).
The proposed fix makes sure metadata is pre-populated (based on https://github.com/dpkp/kafka-python/blob/4d598055dab7da99e41bfcceffa8462b32931cdd/kafka/producer/kafka.py#L579).
I'm just not sure if we should wrap `_wait_on_metadata` into try\except, maybe just passing Exception to the caller would be a better idea...

instrumentation/opentelemetry-instrumentation-kafka-python/src/opentelemetry/instrumentation/kafka/utils.py

@@ -2,6 +2,7 @@
 from logging import getLogger
 from typing import Callable, Dict, List, Optional
 
+from kafka.errors import errors as KafkaErrors
 from kafka.record.abc import ABCRecord
 
 from opentelemetry import context, propagate, trace
@@ -146,6 +147,10 @@ def _traced_send(func, instance, args, kwargs):
             kwargs["headers"] = headers
 
         topic = KafkaPropertiesExtractor.extract_send_topic(args, kwargs)
+        try:
+            instance._wait_on_metadata(topic, instance.config['max_block_ms'] / 1000.0)
+        except KafkaErrors.BrokerResponseError as kafka_exception:
+            _LOG.exception(kafka_exception)
         bootstrap_servers = KafkaPropertiesExtractor.extract_bootstrap_servers(
             instance
         )