Migrate `pallet-authority-discovery` to umbrella crate #9513

Job	Run time
preflight / preflight	42s
preflight / ci-versions	59s
cargo-check-benches (master)	1m 33s
cargo-check-benches (current)	1m 28s
test-frame-ui	1m 33s
cargo-check-each-crate (1)	1m 25s
cargo-check-each-crate (2)	1m 24s
test-full-crypto-feature	1m 25s
cargo-check-each-crate (3)	1m 29s
test-node-metrics	1m 24s
cargo-check-each-crate (4)	1m 27s
cargo-check-each-crate (5)	1m 29s
cargo-check-each-crate (6)	1m 25s
cargo-check-all-crate-macos	52s
cargo-check-each-crate (7)	1m 23s
test-frame-examples-compile-to-wasm	0s
test-deterministic-wasm	0s
check-tracing	0s
check-metadata-hash	0s
node-bench-regression-guard	6s
All test misc tests passed	1s
	20m 5s

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