Add support for shutdown variables, mode selector, PC reset timing, and battery switch threshold

- Introduced new variables to the phoenixcontact_modbus driver especially for QUINTS 4 USB:
  - shutdown variables
  - mode selector 9 = PC_MODE
  - PC reset delay after main power recovers
  - automatic switch to battery mode if main power is below or above a defined threshold.

Signed-off-by: haul <[email protected]>

Author: haul