关于 gcp pubsub 的介绍
https://cloud.google.com/pubsub/?hl=zh-cn
添加依赖：
<dependency>
<groupId>org.apache.flink</groupId>
<artifactId>flink-connector-gcp-pubsub_${scala.binary.version}</artifactId>
<version>${flink.version}</version>
</dependency>