Add Child Bounties to Polkadot and Kusama (#4863)

* add to kusama

* polkadot too

* cargo run --quiet --profile=production  --features=runtime-benchmarks -- benchmark --chain=kusama-dev --steps=50 --repeat=20 --pallet=pallet_child_bounties --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --header=./file_header.txt --output=./runtime/kusama/src/weights/

* cargo run --quiet --profile=production  --features=runtime-benchmarks -- benchmark --chain=polkadot-dev --steps=50 --repeat=20 --pallet=pallet_child_bounties --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --header=./file_header.txt --output=./runtime/polkadot/src/weights/

* Update Cargo.lock

* Update runtime/kusama/src/lib.rs

* Update runtime/polkadot/src/lib.rs

* import

Co-authored-by: Parity Bot <[email protected]>