Get all messages from the broker REST-API at once

[LukasPoque]

In the older version of the Broker-REST-API, there was no option to receive all messages in a queue with one GET. Now we added an endpoint for that purpose: https://broker.s3i.vswf.dev/apidoc/#/Broker/get__endpoint__all

This should be supported in the BrokerRestConnector implementation.