Extend Load Script with GET_TXN

As of now, GET_TXN doesn't support State (Audit) Proofs, and requires to be sent to all nodes and waiting for f+1 equal replies.

GET_TXN may be used a lot in some cases, so we need to evaluate max performance the pool can handle with GET_TXN.

Acceptance criteria

• Extend load script to be able to send GET_TXN
• It needs to be possible to use GET_TXN to get UTXO (the most common case)