Bosch BTH-RA: reimplemenation of "auto mode"

[dierochade]

With this merged commit d91e2f3 the bosch thermostat no longer provides the system modes 'heat', 'off', and 'auto' but only 'heat' and 'off'. This was done because the device internal schedule cannot be adjusted or even deleted with z2m (at the moment).

However, this should be reverted back to all three modes:

• The device does provide this mode, so it would be the normal decision to expose it too
• It even has a hardware button/dial to select the auto mode, it also has a dedicated element in the segmented display to show this mode
• If the device is in auto mode, it is reported as unknown in home assistant, what is kind of misleading
• only auto mode (along with 'heat' and 'off' mode) give the full functionality. It can be useful, even if the built in schudele interferes, e.g.: If the changes of the schedule in auto mode are just catched and reverted by an automation, you are able to have an normal auto mode and the possibility to switch in manual mode directly at the device.
• the removal was a hard breaking change, if all modes have been used in the past

The change was suggested here #6995 without participation so far.

[dierochade]

@DerDreschner
As you have effectively provided all the code and made this work for us (Thank you very much!!), I would like to ask you about your opinion on this.

[Koenkk]

Looks good, will merge after review from @DerDreschner

[dierochade]

@Koenkk
Do you think we could proceed with this?

[Koenkk]

Thanks!