Import school terms and validity ranges

Blocked by AlekSIS#40 and AlekSIS-App-Chronos#85 (closed)

added part::backend type::refactoring workflow::blocked labels

changed title from Import school years and validity ranges to Import school terms and validity ranges

removed workflow::blocked label

assigned to @hansegucker

created merge request !24 (merged) to address this issue

mentioned in merge request !24 (merged)

closed via merge request !24 (merged)