[FEAT] Rename to Luanti

[stateisbad]

Is this a new feature request?

• I have searched the existing issues

Wanted change

Not really a bug or feature, but Minetest has begun rebranding to Luanti. With the release of 5.10.0, the console startup message reads as Luanti. Also, the server list has started rebranding, too. It's probably time to consider when/how to rebrand this repo/image as well. Thanks for all your hard work!

Reason for change

Upstream rebrand.

Proposed code change

No response

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