[feat] Add support for '/' in MQTT prefix

[kipe]

Is your feature request related to a problem? Please describe.
Currently the prefix for MQTT topics only allows "a-z", "A-Z", "0-9", and "_". With the current prefix limitations, it's not possible to just subscribe to zwavejs2mqtt/+/# (for example, using zwavejs2mqtt/uuid as prefix). This would be useful when implementing a server with multiple zwavejs2mqtt instances connected, allowing the prefix to differentiate instances from each other.

Describe the solution you'd like
By allowing "/" as part of prefix, it would be possible use prefixes such as zwavejs2mqtt/55976116-d9f0-4c16-891c-e6bd771f550d. This would allow for more simple listener subscriptions.

Describe alternatives you've considered
Currently I'm subscribing to each "prefix-topic" separately, using prefixes like zwavejs2mqtt-55976116-d9f0-4c16-891c-e6bd771f550d. This requires subscriptions to each instance of zwavejs2mqtt separately.