Allow to create topics to write to in the adapter config

[foxriver76]

Is your feature request related to a problem? Please describe. If you want to write to a topic, that never receives data, the datapoint is never created by the adapter. Workarounds are, that users create them with scripts or admin adapter. However, also admin forces special structure, like no top level states. Also we should not make special cases for adapter X and Y in admin.

Describe the solution you'd like MQTT adapter provides e.g. a table in the config, where users can create topics, which they want to write to. At adapter start, MQTT will ensure all table entries have a datapoint at adapter start.

Describe alternatives you've considered Hard coded allowance to for completely free structure in admin adapter for special adapters via io-pack flag or hard coded. However, I do not think, that these approaches should be taken.

Additional context https://github.com/ioBroker/ioBroker.admin/issues/1067