Migrate `pallet-indices` to umbrella crate #17189

Job	Run time
check-dependency-rules	9s
check-fail-ci	14s
check-markdown	14s
check-readme	3m 2s
check-workspace	16s
preflight / preflight	1m 20s
preflight / ci-versions	52s
fmt	1m 5s
check-rust-feature-propagation	1m 54s
check-toml-format	59s
check-umbrella	2m 10s
test-rust-features	1m 52s
All quick checks passed	1s
	14m 8s

Provide feedback