Docs miss a general section about how to set event metadata

[mfelsche]

Users asked us for help on how to set event metadata for a specific connector. It should be clear from the docs how to do this, lets improve here.

Hint: via $ path. That path refers to a record that can be manipulated. Connector-specific metadata always is stored under the prefix $<CONNECTOR_TYPE>. at this key you can always expect a record with further options, detailed in the connectors documentation.