Make pallet-recovery supports `BlockNumberProvider`.

Part of #6297.

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Polkadot address: 156HGo9setPcU2qhFMVWLkcmtCEGySLwNqa3DaEiYSWtte4Y

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Co-authored-by: Guillaume Thiolliere <guillaume.thiolliere@parity.io>
Co-authored-by: GitHub Action <action@github.com>