Add multiplayer-bomber example. #2873

Job	Run time
clippy	1m 59s
doc-lints	51s
rustfmt	18s
godot-itest (macos)	1m 26s
license-guard	29s
godot-itest (windows)	2m 54s
run-examples	1m 41s
godot-itest (linux-full)	2m 24s
unit-test	2m 35s
godot-itest (linux-features-experimental)	2m 46s
godot-itest (linux-4.1)	1m 13s
godot-itest (linux-4.2)	1m 43s
godot-itest (linux-memcheck)	2m 8s
ci-status	4s
	22m 31s

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