Support for "has_built_in_endstop" parameter from time_based_cover

[mrflo97]

Would it be possible to add the config parameter "has_built_in_endstop" used in default ESPHome Time based cover?

With this it would be possible to fix out any miscalculation of the current position by just letting the blinds close or open fully.

[bruxy70]

I guess it should be possible, and I suppose not adding it would behave the same as today, so this should not be a breaking change. So feel free to add it.
Cheers
V