[hdpowerview] Bridge handler dynamic channel refactoring

[jlaur]

The bridge handler class HDPowerViewHubHandler has grown after:

• [hdpowerview] Add support for scene groups #11534
• [hdpowerview] Add support for enabling/disabling automations #11637

Especially the logic for creating automation channels is quite large (> 100 lines) and should be extracted to a separate class. This will improve the readability of the class by removing some responsibilities also make it easier to cover by unit tests.