Additional RPC for dumping all main storage key pairs under a prefix (#4803)

* Merge branch 'gav-split-balanecs-vesting' into gav-upsub

# Conflicts:
#	Cargo.lock
#	cli/Cargo.toml
#	collator/Cargo.toml
#	primitives/Cargo.toml
#	runtime/common/Cargo.toml
#	runtime/common/src/claims.rs
#	runtime/kusama/Cargo.toml
#	runtime/polkadot/Cargo.toml
#	service/Cargo.toml

* Update client/src/client.rs

* Update client/src/client.rs

* Fix merge conflict

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>