Update Release Notes

[stefanmore]

I propose we streamline the process for creating and updating a changelog and/or release notes.

The state right now:

• latest release in release notes on https://technology.a-sit.at/pdf-over-2/ is 4.4.3.1 (current release is 4.4.7)
• no release notes in https://github.com/a-sit/PDF-Over/tags
• no releases on https://github.com/a-sit/PDF-Over/releases

[kathrin-7978]

• created releases from 4.4.0 to 4.4.7 incl. release notes
• removed release notes from https://technology.a-sit.at/pdf-over-2/, link to github instead
• add release.yml for automated release build: automate release build #173