Create config split for drupal.at

Problem/Motivation

Create a separate split for the future drupal.at website. Base the configs on the drupal.de split.

Steps to reproduce

The current version of the Austrian website is drupal-austria.at. The split should be prepared to ensure drupal.at has all the necessary basic configurations to start with.

Proposed resolution

Create a separate split and add the following basic changes (more to be added after discussing):

• All addresses use Austria as a default country
• The DE language is added and the translations are accessible using the de URL prefix
• The site information and timezone

Remaining tasks

To be added

User interface changes

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API changes

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Data model changes

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