Add temperature offsets

[CSchlipp]

This PR adds two optional configuration values in the yaml for outside & current temperature offsets.

current_temperature_offset: 0
outside_temperature_offset: 0

The offsets are added to the temperature readings and internally subtracted from the target temperature settings.
Examples:

• If the temperature is actually higher than measured by the AC, set the difference as a positive offset.
  • E.g. actual temperature = 23°, AC measured temperature = 20° --> offset = 3°
    • current temperature is reported as 23°
    • target temperature sent to the AC is reduced by 3°, so that the AC is not heating beyond actual temperature
      • target temperature set to 23° will internally be sent as target = 20° to the AC (which corresponds to the actual temperature of 23°)
• If the temperature is actually lower than measured by the AC, set the difference as a negative offset.
  • E.g. actual temperature = 20°, AC measured temperature = 22° --> offset = -2°
    • Current temperature is reported as 20°
    • target temperature sent to the AC is reduced by -2° (=increased by 2°), so that the AC heats more to reach the actual temperature
      • target temperature set to 20° will internally be sent as target = 22° to the AC (which corresponds to the actual temperature of 20°)

Tested only with CNT variant.

[Noki]

@DomiStyle can we get this merged?