add subchart for whiteboard backend

[Wopf]

Description of the change

As the whiteboard app in hub9 onward is promoted to have an internal back end service, it'll be cool to have it's deployment routine (aka sub chart) integrated in this chart.

Benefits

Get the whiteboard back end running by easily editing a few lines in your values.yaml files on kubernetes based setups.

Possible drawbacks

Don't see any

Additional information

Would be cool to have kinda feature toggle

whiteboardBackendService:
  enable: true

in the values.yaml evaluated in the Chart.yaml

[s0undy]

+1 This would be a nice feature!