Allow users to pay for transaction fees using predicates

[luizstacio]

Users have to use their Wallet to pay for a transaction. However, there are many use cases where a user wants to pass a Predicate, instead of a Wallet, to pay for a transaction. The actual UTXOs used to pay for the transaction must be unlocked in the predicate passed.

For example:

const contract = ExampleContractAbi__factory.connect(wallet);

let response = await contract
    .functions
    .initialize_counter(42) // Build the ABI call
    .call() // Perform the network call

Here, we link a Wallet to the contract instance. Underneath, it will grab this wallet's funds to pay for the transaction.

With this new feature, one could pass in a Predicate instead of a Wallet, and, underneath, the predicate would be evaluated, and, if true, the UTXOs unlocked would be used to pay for the tx fees.

This is based by a feedback we got from an external developer, here's what was said about this feature request:

When I want to spend utxos from a predicate, there should be a wallet that offers the same kind of features as a wallet for a simple public key address. Currently, you need to initialize the wallet with a key, and that will also be the address that pays for the fees. If I have a predicate, I generally want to pay for the fees with the coins available in the utxos on the predicate address. A public-key based address should not be required to manage a predicate wallet.

Base issue: FuelLabs/fuels-rs#809

[arboleya]

@luizstacio How is this issue different from this other one?

• Add test for using proceeds of Predicate in a Script call #757

cc @camsjams

[luizstacio]

Issue #757 would include tests using a predicate to execute script call. Once this issue is done and scripts are done, it would be possible to implement tests for calling a Script using Predicate as a Wallet, closing the issue #757.