Method to start modules from a defined state

[sandtreader]

As part of enabling testing from Haskell 'golden tests' we need a way to get modules to boot from a given ledger state. The state will be in a CBOR file specific to that module, and read (for now) through manual minicbor decoding, although the intention is use a CDDL workflow to code generate in time.

State will be sent to each module with a message, subscription to which is only enabled in test frameworks.