No topics are captured in the Broker Hierarchy for brokers that deny subscription to #

[Steve-Mcl]

Current Behavior

Some Brokers do not permit subscribing to # and therefore the Broker Hierarchy never gets populated with any topics

In particular, EMQX (by default), Azure IoT Hub, AWS IoT Core and many others do not permit subscribing to #

Expected Behavior

We may wish to include a topic filter on the broker configuration.
We may also want to consider

• an admin setting that allows/prevents a min top level topic (to avoid hammering the DB if/when someone subscribes to a public broker)
• a deny list to prevent public brokers being added to as a BYOB entry?

Steps To Reproduce

Try adding an emqx broker (that by default does NOT return anything on #) - no topics are populated.

Environment

• FlowFuse version: FFC Current
• Node.js version:
• npm version:
• Platform/OS:
• Browser:

Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

[joepavitt]

Will scope this to adding a config option in the Broker settings to define the top-level scope that you wish to subscribe to for traffic, defaulting to # (for now)