Protocol Gateway Template: close connections to AMQP adapter if no device is connected

[b-abel]

Currently, the protocol gateway template opens one AMPQ connection to Hono for each tenant that has devices connected to it. When the last device connection for a tenant is closed it would be good to close the corresponding AMQP connection as well.

[calohmn]

As part of working on the connection handling here, it would be good to also consider using a timeout for the handleEndpointConnection() request triggering the initial connection establishment to the AMQP adapter for a tenant. The result of factory.connect could be decoupled from the connectGatewayToAmqpAdapter return value here, using an isConnected(timeout) check for the return value instead.