[Feature]: Check the input scriptPubKey when fetchingg signers' UTXO

[djordon]

Feature - Check the input scriptPubKey when fetching signers' UTXO

1. Description

When searching for the signers outstanding UTXO in #538, we need to only include transactions where one of the inputs points to an output matching one of the signers' scriptPubKeys. Anyone can create an output that the signers' control, but we are only interested in transactions that we know the signers have created. This check is necessary because without it, we could fetch a UTXO that the signers have not created.

1.1 Context & Purpose

We need to update the list of criteria in #538 to specify that we are only interested in transactions where a transactions prevout was signed for by the signers.

2. Technical Details:

2.1 Acceptance Criteria:

• Make sure that the UTXO was created by the signers.

3. Related Issues and Pull Requests (optional):

#538