fix(Kafka backend): use enum values when represent kafka backend as d…

[marcosschroh]

…ict. Close #130

Currently when a Kafka backend is created, enums are not properly represented causing errors when instantiating producers and consumers. We rely on backend.dict() to propagate the kafka configuration: producer instantiation and consumer instantiation

Example:

from kstreams.backends.kafka import  Kafka, SecurityProtocol

kafka_backend = Kafka(
    security_protocol=SecurityProtocol.SASL_PLAINTEXT,
    sasl_plain_username="username",
    sasl_plain_password="pwd",
)

kafka_backend.dict()

{
    'bootstrap_servers': ['localhost:9092'],
    'security_protocol': <SecurityProtocol.SASL_PLAINTEXT: 'SASL_PLAINTEXT'>,  # WRONG 
    'ssl_context': None,
    'sasl_mechanism': <SaslMechanism.PLAIN: 'PLAIN'>,    # WRONG 
    'sasl_plain_username': 'username',
    'sasl_plain_password': 'pwd',
    'sasl_oauth_token_provider': None
}

print(Kafka(sasl_mechanism='PLAIN').sasl_mechanism) 
# <SaslMechanism.PLAIN: 'PLAIN'>

This patch will fix the dict representation:

{
   'bootstrap_servers': ['localhost:9092'],
    'security_protocol': 'SASL_PLAINTEXT',  # Expected by aiokafka
    'ssl_context': None,
    'sasl_mechanism': 'PLAIN',  # Expected by aiokafka
    'sasl_plain_username': 'username',
    'sasl_plain_password': 'pwd',
    'sasl_oauth_token_provider': None
}


assert Kafka(sasl_mechanism='PLAIN').sasl_mechanism) == 'PLAIN'

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02% 🎉

Comparison is base (28a377d) 94.10% compared to head (f9823d0) 94.12%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #131      +/-   ##
==========================================
+ Coverage   94.10%   94.12%   +0.02%     
==========================================
  Files          20       20              
  Lines         712      732      +20     
==========================================
+ Hits          670      689      +19     
- Misses         42       43       +1     

Flag	Coverage Δ
unittests	94.12% <100.00%> (+0.02%)	⬆️

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Files Changed	Coverage Δ
kstreams/backends/kafka.py	96.07% <100.00%> (+0.07%)	⬆️

... and 1 file with indirect coverage changes

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