Add customizable WebSocket subprotocol selection #6029

Job	Run time
external-types	29s
cargo-hack	1m 15s
Spell Check with Typos	6s
check (.)	35s
dependencies-are-sorted	7s
cargo-deny check (advisories)	22s
check (examples)	35s
check-docs	28s
cargo-deny check (bans licenses sources)	20s
test-msrv	2m 9s
test-docs	50s
wasm32-unknown-unknown	14s
armv5te-unknown-linux-musleabi	25s
test-versions (beta, .)	47s
test-nightly	1m 1s
test-versions (beta, examples)	37s
test-versions (stable, examples)	38s
test-versions (stable, .)	44s
	11m 42s

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