Improve kafka-python instrumentation examples (#3388)

* Improve kafka-python instrumentation example

* Improve kafka-python instrumentation examples

Author: andremm

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

@@ -30,10 +30,14 @@
     producer = KafkaProducer(bootstrap_servers=['localhost:9092'])
     producer.send('my-topic', b'raw_bytes')
 
+    def process_msg(message):
+        print(message)
+
     # report a span of type consumer with the default settings
     consumer = KafkaConsumer('my-topic', group_id='my-group', bootstrap_servers=['localhost:9092'])
     for message in consumer:
-    # process message
+        # process message
+        process_msg(message)
 
 The _instrument() method accepts the following keyword args:
 tracer_provider (TracerProvider) - an optional tracer provider
@@ -53,6 +57,7 @@ def consume_hook(span: Span, record: kafka.record.ABCRecord, args, kwargs)
     def produce_hook(span, args, kwargs):
         if span and span.is_recording():
             span.set_attribute("custom_user_attribute_from_produce_hook", "some-value")
+
     def consume_hook(span, record, args, kwargs):
         if span and span.is_recording():
             span.set_attribute("custom_user_attribute_from_consume_hook", "some-value")
@@ -65,6 +70,14 @@ def consume_hook(span, record, args, kwargs):
     producer = KafkaProducer(bootstrap_servers=['localhost:9092'])
     producer.send('my-topic', b'raw_bytes')
 
+    def process_msg(message):
+        print(message)
+
+    consumer = KafkaConsumer('my-topic', group_id='my-group', bootstrap_servers=['localhost:9092'])
+    for message in consumer:
+        # process message
+        process_msg(message)
+
 API
 ___
 """