Returns the storage at the given block height and transaction index. The result can be paged by providing a maxResult to cap the number of storage slots returned as well as specifying the offset via keyStart (hash of storage key).
blockHash: STRING - The hash of the block
txIndex:INTEGER - The transaction index for the point in which we want the list of accounts
address: STRING - The contract address
startKey: STRING - The offset (hash of storage key)
maxResult: STRING - The number of storage entries to return