add generic-aarch64 platform for ARM-based virtual appliances

[jens-maus]

Description

This PR adds a new generic-aarch64 platform which will generate images that can be used with e.g. virtual platforms like ProxmoxVE on ARM (cf. https://github.com/jiangcuo/Proxmox-Port) to run RaspberryMatic as a virtual appliance on a ARM-based (especially the powerful RaspberryPi5) kind of hardware.

Related Issue

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Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Alternate Designs

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Possible Drawbacks

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Verification Process

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Release Notes

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Contributing checklist

• My code follows the code style of this project.
• I have read the CONTRIBUTING and LICENSE document.
• I fully agree to distribute my changes under Apache 2.0 license.