Allow only specific team roles to be initailized to owners #1082

Job	Run time
Clippy	48s
Rustfmt	10s
Test (MSRV)	1m 17s
Build docs	1m 22s
Test (stable)	2m 1s
Test (beta)	2m 9s
Test (nightly)	1m 41s
Test (macOS)	1m 51s
Test (Windows)	4m 48s
Test (no features)	1m 13s
Test (all features - simdjson, cargo test --all-features --lib --tests --examples)	1m 9s
Test (native TLS, cargo test --all-features --features serenity/native_tls_backend --lib --tests ...	1m 22s
	19m 51s

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