[FEATURE]: Configuration via fixed update/calibration-time (alternativ to periods)

[Stopuhr]

In some use cases/environments, the updates and calibrations should be a fixed times. If updates are not needed hourly, they should be independent from the os-startup-time.

Possible solution:
When using ':' the value is used as time and not period.

Maybe better solution:
New concurrent configuration-list of update-times, each entry with an optional attribute 'doCalibration'.

This last solution could also support an other optimization that updates only, when changes are found: attribute 'skipIfUnchanged'.

[github-actions]

Hi there and welcome to Inkycal. Thanks for opening this issue. As this is your first issue in this repository, please read through the contributing guidelines