Block & fail early if produce requests don't work

[grdryn]

The kafka-python docs[1] note that producer.flush() only blocks
until all messages are put on the network, and it doesn't guarantee
delivery or success. Even if the provided credentials correspond to a
principal that doesn't have permission to produce to the topic,
everything might look like it has succeeded to the user:

>>> produce_messages(1, 10, 2)
sending {"txt": "hello 1"}
sending {"txt": "hello 2"}
sending {"txt": "hello 3"}
sending {"txt": "hello 4"}
sending {"txt": "hello 5"}
sending {"txt": "hello 6"}
sending {"txt": "hello 7"}
sending {"txt": "hello 8"}
sending {"txt": "hello 9"}
sending {"txt": "hello 10"}

The change proposed here (also based on the docs[1]) will cause each
iteration of the loop to block until the produce request has either
succeeded or failed:

>>> produce_messages(1, 10, 2)
sending {"txt": "hello 1"}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 25, in produce_messages
  File "/var/home/gryan/.local/lib/python3.10/site-packages/kafka/producer/future.py", line 65, in get
    raise self.exception # pylint: disable-msg=raising-bad-type
kafka.errors.TopicAuthorizationFailedError: [Error 29] TopicAuthorizationFailedError: python-test

NOTE: I haven't actually tried this notebook out, as I don't know how
to run notebooks yet and haven't set up an environment for that -- I
was just trying to understand why a buddy was not seeing a failure
when they should have, when running the code from this notebook. I
just copied the code from here into my local python interpreter. I
don't know if there's any special way that exceptions should be
handled in notebooks or anything like that.

[1] https://pypi.org/project/kafka-python/

[grdryn]

@cfchase Hi! 👋 You seem to be the owner of this project, so just pinging you about this in case you don't have notifications turned on for all activity here. 🐻

[k-wall]

@grdryn thanks for taking the initiative and offering the fix. (which lgtm btw)

[cfchase]

@grdryn thanks for submitting this! Sorry I just noticed. I'll test it out and get it merged.