`candidate-validation`: RFC103 implementation (#5847)
Part of https://github.com/paritytech/polkadot-sdk/issues/5047 On top of https://github.com/paritytech/polkadot-sdk/pull/5679 --------- Signed-off-by: Andrei Sandu <[email protected]> Co-authored-by: GitHub Action <[email protected]>