Add contract deployment transaction

[ureeves]

Summary

A transaction type should be added to deal with the deployment of contracts. This is necessary for a contract deployment system to be able to function in the context of phoenix.

The transaction type should allow for charging the transaction, as well as deploying a contract - meaning it should include all the relevant data and metadata to perform this.

Possible solution design or implementation

A possible way to tackle this is to replace the Transaction::call field by a new field - maybe called exec - that contains an enum that can either be a contract call, or a contract deployment.

struct Transaction {
    /* other fields */
    exec: Execution,
}

enum Execution {
    Call { /*fields*/ }
    Deploy { /*fields*/ }
}

Additional context

Upstream should be able to use the data of this transaction to charge the user, as well as make decisions on how much to charge. This means the fields of the new transaction should likely be public, or otherwise accessible.

[moCello]

Closed as no longer relevant after #175