`security_protocol` argument docstring does not mention `SASL_SSL` or `SASL_PLAINTEXT`

[gabrielmbmb]

Describe the bug

The security_protocol argument docstring in aiokafka.{AIOKafkaConsumer, AIOKafkaProducer} does not mention SASL_SSL and SASL_PLAINTEXT as possible values but they are as mentioned in the sasl_mechanism argument docstring.

https://github.com/aio-libs/aiokafka/blob/57439a6dfacabbd8fe591cafb6d116224a8132da/aiokafka/producer/producer.py#L140-L142

https://github.com/aio-libs/aiokafka/blob/57439a6dfacabbd8fe591cafb6d116224a8132da/aiokafka/consumer/consumer.py#L170-L171

aiokafka.client.AIOKafkaClient does mention all the possible values:

https://github.com/aio-libs/aiokafka/blob/57439a6dfacabbd8fe591cafb6d116224a8132da/aiokafka/client.py#L77-L79

Expected behaviour security_protocol argument docstring mentions SASL_SSL and SASL_PLAINTEXT as possible values.

Environment (please complete the following information):

• aiokafka version (python -c "import aiokafka; print(aiokafka.__version__)"): 0.8.0
• kafka-python version (python -c "import kafka; print(kafka.__version__)"):
• Kafka Broker version (kafka-topics.sh --version):
• Other information (Confluent Cloud version, etc.):