Add `getStorageProof` endpoint

[ArielElp]

The Starknet state commitment consists of three Merkle-Patricia tries (read more here) :

• global state (leaf is a contract address)
• classes (leaf is the class hash)
• contracts storages (tree per contract)

This endpoint should return the data required to provide storage proofs in each of the relevant trees. Known use cases include:

• storage proofs
• running the starknet OS

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This change is