Add multiplayer-bomber example. #2876

Job	Run time
doc-lints	50s
rustfmt	23s
clippy	1m 46s
godot-itest (macos)	1m 41s
license-guard	33s
godot-itest (windows)	2m 30s
run-examples	1m 15s
godot-itest (linux-full)	2m 23s
unit-test	2m 38s
godot-itest (linux-features-experimental)	2m 14s
godot-itest (linux-4.1)	1m 13s
godot-itest (linux-4.2)	1m 11s
godot-itest (linux-memcheck)	2m 11s
ci-status	3s
	20m 51s

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