Rely on a configMap for operator-level settings

[sebgl]

Forked from #2791.

The number of flags that can be passed to the operator binary is becoming quite large. It may feel more natural for users to tweak them through a configMap rather than modifying the operator StatefulSet spec. Providing a default config with comments explaining each setting would also make the possible options easier to understand.

Should we setup a mechanism to auto-reload the config, or auto-kill/restart the operator when the configuration changes, or should we let users deal with it?

[pebrc]

Another aspect here is that when ECK is installed via Operator Lifecycle Manager users typically do not have the ability to tweak startup flags but a auto-reloaded configuration file would be a way to work around that restriction.