Optimize contract's graphql queries

[arboleya]

During some load tests, we realized a couple of issues (#3279, #3277) that we're fixing and optimizing.

In keeping with this theme, we should continue the effort and review our predefined GQL queries and fragments.

Every field removal is a breaking change and can break things for apps, so we need to be extra careful here.

Taking from the providers/operations.graphql:

• getContract
• getContractBalance

[nedsalk]

Took a look at this and the queries don't look like they could be optimized further.

"""
from fuel-core-schema.gql
"""
type Contract {
  id: ContractId!
  bytecode: HexString!
  salt: Salt!
}

type ContractBalance {
  contract: ContractId!
  amount: U64!
  assetId: AssetId!
}

"""
from operations.graphql
"""
fragment contractBalanceFragment on ContractBalance {
  contract
  amount
  assetId
}

query getContract($contractId: ContractId!) {
  contract(id: $contractId) {
    bytecode
    id
  }
}

query getContractBalance($contract: ContractId!, $asset: AssetId!) {
  contractBalance(contract: $contract, asset: $asset) {
    ...contractBalanceFragment
  }
}

All the data queried via these queries is utilized in the places where the queries are used, so there's no place for more optimization.