Add migration to clear unapproved proposals from treasury pallet #2656

Job	Run time
preflight / preflight	33s
preflight / ci-versions	57s
cargo-check-benches (master)	25m 31s
cargo-check-benches (current)	28m 25s
cargo-check-all-crate-macos	10m 44s
cargo-check-each-crate (1)	21m 31s
test-frame-ui	25m 47s
cargo-check-each-crate (2)	18m 35s
cargo-check-each-crate (3)	5m 7s
test-full-crypto-feature	2m 35s
cargo-check-each-crate (4)	18m 22s
test-node-metrics	11m 40s
cargo-check-each-crate (5)	26m 21s
cargo-check-each-crate (6)	12m 59s
cargo-check-each-crate (7)	29m 18s
test-frame-examples-compile-to-wasm	2m 55s
test-deterministic-wasm	7m 35s
check-tracing	2m 36s
check-metadata-hash	6m 42s
node-bench-regression-guard	13s
All test misc tests passed	1s
	4h 18m 27s

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