Added: support sasl/scram authentication

[mingqing]

kafka client connect broker support SASL/SCRAM-* authentication, for example:

export KAFKA_BROKER_LIST="kafka1:9092,kafka2:9092,kafka3:9092"
export KAFKA_TOPIC="metrics"
export KAFKA_SECURITY_PROTOCOL="sasl_plaintext"
export KAFKA_SASL_MECHANISM="SCRAM-SHA-256"
export KAFKA_SASL_USERNAME="uptime"
export KAFKA_SASL_PASSWORD="testkey"

./prometheus-kafka-adapter

[palmerabollo]

Thanks for your contribution 🎉 , looks good to me. Let's see if @jpfe-tid wants to add something else, otherwise I'll merge it and release a new version in a couple of days.

[jpfe-tid]

Thanks for your PR, @mingqing ! 🚀

I've added some rewrite suggestions to avoid conflicts in config.

[mingqing]

Is it necessary to main.go "traefik/log" in is replaced by "logrus"? @jpfe-tid

[jpfe-tid]

@mingqing thanks for noticing, we'll fix it by using only one logging package in the next PR (WIP), meantime we'll merge this PR.