Merge branch 'release-2.2a0' into 'master'

Bump version to 2.2a0

See merge request AlekSIS/official/AlekSIS-App-Untis!135

pyproject.toml

 [tool.poetry]
 name = "AlekSIS-App-Untis"
-version = "2.1.4.dev0"
+version = "2.2a0"
 packages = [
     { include = "aleksis" }
 ]