Reconcile sandbox transaction validator with MongoDB implementation

[sync-by-unito]

h3. Statement of Problem

For testing and running in a local sandbox environment, a separate set of validators should be created to replicate the updates from Bifrost transactions that are either sent or mocked responses from a Bifrost node.

h3. Acceptance Criteria

• A validator that can accept mock transaction responses
• Unit test for sending mock transactions to the validator and checking the result is a valid update

┆Issue is synchronized with this Jira Task by Unito