[Broker] Known Connectors Feature

[SebastianOpriel]

The current implementation allows to set a list of Connectors to be crawled. This feature should be separated from the Broker-Server-Extension in an own extension and be added to the EDC UI. Goal is to have one Extension for EDC UI users to manage a "Known Connectors" friend list (as new tab in connector), which will be reflected e.g. in Catalog crawling. On the other hand, Broker Server Extension shall use this extension to manage the known connectors. So its simply an extraction of a feature to use it for both, broker-server-extension as well as standalone in EDC.