Expose ability to obtain ContractPackageHash of new locked contract

Creating a locked contract package is currently hidden behind `new_locked_contract,` which only returns a `ContractHash.` To create entrypoints with group restrictions, we first need to create a contract package, then create a group, then we can create restricted entrypoints.

Reference:

https://github.com/casper-network/casper-node/blob/7c9b7a7df1affa75d29c97f0e141f29d0df415d6/smart_contracts/contract/src/contract_api/storage.rs#L152-L167. We should make this public.