BIRD2: New Appliance

[ghost]

This is my BIRD2 appliance, based on Debian 12 (Bookworm), as announced in issue #501. It replaces the outdated BIRD appliance.

I set the image location to http://downloads.sourceforge.net/project/gns-3/Qemu%20Appliances/bird2-debian-2.0.12.qcow2.

As I can't upload to that location, I put it temporarily in https://github.com/b-ehlers/gns3-registry/releases/download/BIRD2/bird2-debian-2.0.12.qcow2, @grossmj please upload it to the final location.

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Before submitting a pull request, please check the following.

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When updating an existing appliance:

• The new version is on top.
• The filenames in the "images" section are unique, to avoid appliances / version overwriting each other.
• If you forked the repo, running check.py doesn't drop any errors for the updated file.

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When creating a new appliance:

• It's tested locally, i.e.
  • You dragged an instance into a project on your box, got it installed (if necessary), and did some basic network checks (ping, UI reachable, etc.).
  • GNS3 VM can run it without any tweaks.
  • The device is in the right category: router, switch, guest (hosts), firewall
  • You filled in as much info as possible (checks the schemas and other appliance files for some guidance).
• When adding a container: it builds on Docker Hub and can be pulled.
• The filenames in the "images" section are unique (to avoid appliances and/or versions overwriting each other).
• If you forked the repo, running check.py doesn't drop any errors for the new file.
• Optional: a symbol has been created for the new appliance.

[grossmj]

Thanks! I am away this week, I will merge your PR once I can upload the file on source forge.