Werk #15213: rest_api: time_period exception/active time_ranges default

When creating a time_period via the REST-API, the exception time_ranges field is not required, however if it's not provided, it will raise a key error. This werk adds an empty list as a default value, which aligns with the interface functionality of allowing an empty time_range value. The second fix is the same issue but for the active time_ranges field.

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