Werk #15553: time_period: making time-related validation more strict

Prior to this werk, the REST API was quite lenient when it came to specifying a time allowing the format hh:mm for some while asking the hh:mm:ss format for others. This werk targets the active_time_ranges field where now a hh:mm:ss format is enforced.

Due to the introduction of the more strict pattern, user scripts must be adjusted accordingly to respect the new format.

To the list of all Werks