caconfig-mock-plugin: Support writing nested configurations and configuration collections

currently it's quite cumbersome to persist nested context-aware configurations in unit tests, as the helper methods in MockContextAwareConfig.writeConfiguration* only support writing single configurations and configurations lists without nested structures.

without changing the API signatures of those, it should be supported that the maps passed to this helper methods contain:

• nested maps which are persisted as nested configurations with the given key
• nested lists with maps with are persisted as nested configuration lists with the given key