Add support for Apache Kafka log source

[wanmail]

Why use Apache Kafka

In our environment, it is difficult for me to deploy a local log analysis tool directly on the machine. Fortunately, they have collected the logs into Kafka. I only need to consume them in Kafka.

About Unit Test

I wrote a simple unit test with reference to TestFileStreamRead. But I started a Kafka container locally before running the unit test, so the unit test will fail if directly make check test.

But I have been running it in our production environment for a week, and process about 100 million Kafka messages every day.

About not using waker

Each message in Kafka is a log line, there is no need to use LineReader to find line endings, so I did not use waker.Waker.

Only handled ctx done and network connection error.