fix(cli): helper message default values

[ssheng]

What does this PR address?

Default value in help text is outputting incorrect value from config.

Before:

Options:
  --production                 Run the BentoServer in production mode
  --port INTEGER               The port to listen on for the REST api server  [default: <bound method
                               _ConfigurationItem.get of _ConfigurationItem(_config={'api_server': {'port': 3000,
                               'host': '0.0.0.0', 'backlog': 2048, 'workers': 1, 'timeout': 60, 'max_request_size':
                               20971520, 'metrics': {'enabled': True, 'namespace': 'BENTOML'}, 'logging': {'access':
                               {'enabled': True, 'request_content_length': True, 'request_content_type': True,
                               'response_content_length': True, 'response_content_type': True}}, 'cors': {'enabled':
                               False, 'access_control_allow_origin': None, 'access_control_allow_credentials': None,
                               'access_control_allow_methods': None, 'access_control_allow_headers': None,
                               'access_control_max_age': None, 'access_control_expose_headers': None}}, 'runners':
                               {'batching': {'enabled': True, 'max_batch_size': 100, 'max_latency_ms': 10000},
                               'resources': None, 'logging': {'access': {'enabled': True, 'request_content_length':
                               True, 'request_content_type': True, 'response_content_length': True,
                               'response_content_type': True}}, 'timeout': 300}, 'tracing': {'type': 'zipkin',
                               'sample_rate': None, 'excluded_urls': None, 'zipkin': {'url': None}, 'jaeger':
                               {'address': None, 'port': None}, 'otlp': {'protocol': None, 'url': None}}},
                               _path=('api_server', 'port'))>]
  --host TEXT                  The host to bind for the REST api server [defaults: 127.0.0.1(dev),
                               0.0.0.0(production)]
  --api-workers INTEGER        Specify the number of API server workers to start. Default to number of available CPU
                               cores in production mode
  --backlog INTEGER            The maximum number of pending connections.  [default: <bound method
                               _ConfigurationItem.get of _ConfigurationItem(_config={'api_server': {'port': 3000,
                               'host': '0.0.0.0', 'backlog': 2048, 'workers': 1, 'timeout': 60, 'max_request_size':
                               20971520, 'metrics': {'enabled': True, 'namespace': 'BENTOML'}, 'logging': {'access':
                               {'enabled': True, 'request_content_length': True, 'request_content_type': True,
                               'response_content_length': True, 'response_content_type': True}}, 'cors': {'enabled':
                               False, 'access_control_allow_origin': None, 'access_control_allow_credentials': None,
                               'access_control_allow_methods': None, 'access_control_allow_headers': None,
                               'access_control_max_age': None, 'access_control_expose_headers': None}}, 'runners':
                               {'batching': {'enabled': True, 'max_batch_size': 100, 'max_latency_ms': 10000},
                               'resources': None, 'logging': {'access': {'enabled': True, 'request_content_length':
                               True, 'request_content_type': True, 'response_content_length': True,
                               'response_content_type': True}}, 'timeout': 300}, 'tracing': {'type': 'zipkin',
                               'sample_rate': None, 'excluded_urls': None, 'zipkin': {'url': None}, 'jaeger':
                               {'address': None, 'port': None}, 'otlp': {'protocol': None, 'url': None}}},
                               _path=('api_server', 'backlog'))>]
  --reload                     Reload Service when code changes detected, this is only available in development mode
  --working-dir PATH           When loading from source code, specify the directory to find the Service instance
                               [default: .]
  --ssl-certfile TEXT          SSL certificate file
  --ssl-keyfile TEXT           SSL key file
  --ssl-keyfile-password TEXT  SSL keyfile password
  --ssl-version INTEGER        SSL version to use (see stdlib 'ssl' module)
  --ssl-cert-reqs INTEGER      Whether client certificate is required (see stdlib 'ssl' module)
  --ssl-ca-certs TEXT          CA certificates file
  --ssl-ciphers TEXT           Ciphers to use (see stdlib 'ssl' module)
  -q, --quiet                  Suppress all warnings and info logs
  --verbose, --debug           Generate debug information
  --do-not-track               Do not send usage info
  -h, --help                   Show this message and exit.

After:

Options:
  --production                 Run the BentoServer in production mode
  --port INTEGER               The port to listen on for the REST api server  [default: 3000]
  --host TEXT                  The host to bind for the REST api server [defaults: 127.0.0.1(dev),
                               0.0.0.0(production)]
  --api-workers INTEGER        Specify the number of API server workers to start. Default to number of available CPU
                               cores in production mode
  --backlog INTEGER            The maximum number of pending connections.  [default: 2048]
  --reload                     Reload Service when code changes detected, this is only available in development mode
  --working-dir PATH           When loading from source code, specify the directory to find the Service instance
                               [default: .]
  --ssl-certfile TEXT          SSL certificate file
  --ssl-keyfile TEXT           SSL key file
  --ssl-keyfile-password TEXT  SSL keyfile password
  --ssl-version INTEGER        SSL version to use (see stdlib 'ssl' module)
  --ssl-cert-reqs INTEGER      Whether client certificate is required (see stdlib 'ssl' module)
  --ssl-ca-certs TEXT          CA certificates file
  --ssl-ciphers TEXT           Ciphers to use (see stdlib 'ssl' module)
  -q, --quiet                  Suppress all warnings and info logs
  --verbose, --debug           Generate debug information
  --do-not-track               Do not send usage info
  -h, --help                   Show this message and exit.

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• Does the Pull Request follow Conventional Commits specification naming? Here are GitHub's
  guide on how to create a pull request.
• Does the code follow BentoML's code style, both make format and make lint script have passed (instructions)?
• Did you read through contribution guidelines and follow development guidelines?
• Did your changes require updates to the documentation? Have you updated
  those accordingly? Here are documentation guidelines and tips on writting docs.
• Did you write tests to cover your changes?

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