Citadel support

[chapulina]

This ticket tracks Citadel support for various platforms.

• See all supported platforms for Citadel on this page.
• See the definition of Ignition's support categories on this page.

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Operating System	Architecture	Packaging	CI	Functionality
Ubuntu Bionic	amd64	✅ Yes	✅ Yes, every pull request	✅ All
.	i386	✅ Yes	No	✅ All
.	arm64	❓ Maybe	No	Most low-level libraries known to work
.	armhf	❓ Maybe	No	Most low-level libraries known to work, DART physics engine not available
Ubuntu Focal	amd64	✅ Yes	✅ Yes, every pull request	✅ All
.	arm64	❓ Maybe	No	Most low-level libraries known to work
.	armhf	❓ Maybe	No	Most low-level libraries known to work, DART physics engine not available
MacOS Catalina and BigSur	-	✅ Yes	✅ Yes, every pull request	Ignition only works in headless mode (GUI does not render; instead of using ign gazebo fuel.sdf command, use ign gazebo -s fuel.sdf to start the server only).
Windows 10	.	❓ Maybe	Some libraries tested on every pull request	Command line utilities are not supported. All packages up to but not including ign-gazebo are currently building. DART physics engine is not supported. Qt (GUI functionality) is not supported.

[chapulina]

Removing Buster support since that's EOL.