Improve pallet crowdloan file structure #15615

Job	Run time
check-dependency-rules	9s
check-fail-ci	12s
check-markdown	17s
check-readme	3m 10s
check-workspace	28s
preflight / preflight	46s
preflight / ci-versions	1m 13s
check-rust-feature-propagation	2m 11s
test-rust-features	2m 10s
check-toml-format	1m 17s
check-umbrella	2m 27s
fmt	1m 47s
All quick checks passed	1s
	16m 8s

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