[WIP] Add Multiplayer Example #2869

Job	Run time
license-guard	30s
doc-lints	51s
godot-itest (macos)	1m 8s
clippy	1m 31s
godot-itest (windows)	3m 16s
run-examples	1m 7s
rustfmt	34s
godot-itest (linux-full)	2m 24s
unit-test	2m 28s
godot-itest (linux-features-experimental)	2m 0s
godot-itest (linux-4.1)	1m 23s
godot-itest (linux-4.2)	1m 25s
godot-itest (linux-memcheck)	2m 22s
ci-status	1s
	21m 0s

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