Create central config class for deployer

[jvalkeal]

Yarn deployer is currently designed to work with dataflow server for apache yarn. There is ongoing work to create tasklauncher-yarn sink which can spawn tasks on yarn in a same way than launching those from a dataflow shell.

All configs for dataflow server/deployer is currently done via servers.yml file but in theory tasklauncher-yarn sink can be used with local server. In this case we should have a ConfigurationProperties class in a deployer core which sink could then rely on i.e. for adding whitelisted props.