Add metadata for F-Droid entry

[cyb3rko]

Moin Governikus-Team 👋,
I have noticed the missing icon on https://f-droid.org/de/packages/com.governikus.ausweisapp2/.

So I have added some F-Droid metadata according to this page: https://fdroid.org/en/docs/All_About_Descriptions_Graphics_and_Screenshots/

Some notes about the content:

• Title: "AusweisApp Bund" - Adopted from Google Play Store entry
• Icon: Preview - Same as resources/images/android/playstore_release.png
• Short Description: "Der offizielle eID-Client des Bundes" - Adopted from the GitHub repo description
• Full Description: "Mit der Online-Ausweisfunktion des Personalausweises und des elektronischen
  Aufenthaltstitels können Sie sich im Internet ausweisen." - Current description on F-Droid

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Feel free to change something or give me hints on what to change.

[CLAassistant]

All committers have signed the CLA.