Multi-architecture image for Appswitcher Server

**Is your feature request related to a problem? Please describe.**
The image currently is not available in a multi-architecture variant.
This blocks refarch-templates to implement https://github.com/it-at-m/refarch-templates/pull/1818 and thus to guarantee development possible on non x64 systems.

**Describe the solution you'd like**
Publish images for multiple images (similar to how done in https://github.com/it-at-m/refarch/blob/7d26e6be2fa6ef4998b03b3c106a7344ed65f35a/.github/workflows/build.yml#L70).

**Describe alternatives you've considered**
No alternatives available.

Start by inspecting the repository's existing image build and publishing workflow, then compare it with the referenced refarch .github/workflows/build.yml example around line 70. Confirm which target architectures are required by the linked refarch-templates work; done means the Appswitcher Server image is published as a multi-architecture image and can be consumed on non-x64 systems.

Written by the indexing model from the issue text.