Adding the latest versions of CentOS 7, CentOS 8 and Fedora 35

[Da-Geek]

Before submitting a pull request, please check the following.

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When updating an existing appliance:

• [X] The new version is on top.
• [X] The filenames in the "images" section are unique, to avoid appliances / version overwriting each other.

• [X] If you forked the repo, running check.py doesn't drop any errors for the updated file.

I plan to add CentOS 8-Stream as well as CentOS 9-Stream shortly

[Da-Geek]

When creating a new appliance: Fedora 35-2.1 - commit #218ae0f

• It's tested locally, i.e.
  • [X] 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.).
  • [X] GNS3 VM can run it without any tweaks.
  • [X] The device is in the right category: router, switch, guest (hosts), firewall
  • [X] 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.
• [X] The filenames in the "images" section are unique (to avoid appliances and/or versions overwriting each other).
• [X] 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 a lot 👍