Persist the app state

[marcinc]

Krane is currently stateless and depends on the correct configuration supplied at the app start time. This includes the custom risk rules definitions which are currently expected to be present in a specific location on the filesystem.

The following should be considered:

1. Change example k8s manifests to show how custom risk rules could be loaded from K8s Configmap or PV.

2. Enable Graph persistence to disk via PV. Graph could be then used (at later stage!) to also persist UI choices, whitelists etc, instead of adding another database element to the mix.