[hotfix][docs] refer to kafka_sasl_ssl_example in the docs

[531651225]

• Removing unnecessary transition symbols'/'in the document

'properties.sasl.jaas.config' = 'org.apache.kafka.common.security.scram.ScramLoginModule required username=\"username\" password=\"password\";'

• using transition characters can cause "Value not specified for key 'username' in JAAS config" error,The examples in the document can mislead users

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