Easy setup/customization of Scheduler/Executor

[milenkovicm]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Users should be able to customize scheduler and executors with custom object stores, memory managers and so on ...
removing responsibility from ballista to provide support for much more use cases

Describe the solution you'd like

Provide a way for users to setup/customize scheduler and executor binaries, preferably with few line code changes.

We should try to re-use and adapt current scheduler/executor binaries.

Describe alternatives you've considered

Additional context

provided solution should also be:

• covered with usage examples
• and documentation

[milenkovicm]

will take this