Generalize plugin properties and update them in built-in plugins

## Background
Current setup of properties for plugins is too non-constrictive. Basically allows whatever a plugin creator puts in. Also the kafka properties are then hardcoded.

## Feature
Plugin properties should all start with a predefined prefix for the properties, e.g., `enceladus.kafka.plugin.info-file` and `enceladus.kafka.plugin.err-col`
Properties for kafka should be then stripped off this prefix and as is showed into the properties instance and using for kafka connection. This way when something changes it is adaptable by design.

Locate the plugin-property handling and built-in Kafka plugin entry points; no files or tests are named in the issue, so first trace how properties reach the Kafka connection. Done means plugin properties use the predefined prefix, the prefix is stripped before reaching Kafka, and built-in plugins no longer hardcode Kafka properties.

Scritto dal modello di indicizzazione a partire dal testo della issue.