Replace environment variable for configuration injection

[tweise]

Environment variable OPERATOR_FLINK_CONFIG should be replaced with FLINK_PROPERTIES to support the stock Flink Docker images.

docker-flink/docker-flink#82

We should also update the example to use that image.

[tweise]

Environment variable substitution merged upstream: docker-flink/docker-flink#91

[mwylde]

Is there a way we can make this backwards compatible? Otherwise this will break people's existing images.

[tweise]

Yes, unfortunately it would break images if they were copied from the previous example. On the other hand, the operator will become compatible with the docker-flink images and custom cruft can just be deleted. Should we publish both environment variables for a while or just switch before going out of beta?

[mwylde]

Yeah, I think we would need to do something along those lines. Otherwise this is a breaking change that will be hard to manage for users.