Create CI pipeline

[f1sh1918]

Is your feature request related to a problem? Please describe.
Create a proper ci pipeline for druckerei, backend, flutter apps, release notes, Mattermost notification, etc
Consider that we maybe need release notes different for each app. F.e. we provide multi cards only for sozialpass, so it shouldn't be shown for entitlement card

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[ztefanie]

Closed in favor of #1158