Move dockerfiles to `https://github.com/pinpoint-apm/pinpoint` repository

[ga-ram]

To automate creating and pushing pinpoint docker images for future releases, below folders will be deleted from this repository.

• pinpoint-agent --> Dockerfile will be moved to https://github.com/pinpoint-apm/pinpoint/tree/master/agent
• pinpoint-batch --> Dockerfile is no longer needed with Spring Boot Maven plugin to create the container image
• pinpoint-collector --> Dockerfile is no longer needed with Spring Boot Maven plugin to create the container image
• pinpoint-flink --> Dockerfile will be moved to https://github.com/pinpoint-apm/pinpoint/tree/master/flink
• pinpoint-hbase --> Dockerfile will be moved to https://github.com/pinpoint-apm/pinpoint/tree/master/hbase
• pinpoint-mysql --> removed. It will be substitued with official mysql:8.0 image
• pinpoint-web --> Dockerfile is no longer needed with Spring Boot Maven plugin to create the container image
• pinpoint-zookeeper --> removed