4339 - Submit abft score on chain

[mike1729]

Description

This PR implements PoC of a system that stores abft performance scores on chain. It's meant as a show case of the runtime part using unsigned transactions. The host/client counterpart is important only in one place when it shows how to submit a score.

In current version, the logic ensures that only one score is written to runtime storage every interval (parameter). It's hard to deduplicate transactions with valid next score that eg differs in signature at the transaction pool level. Instead, a softer invariant is provided. Only one tx per block can write a new score. On production, that should suffice since without an adversary, only at most 14 equivalent scores can be in one block, which is not a performance problem. If we expect some forging, we can require signed unsigned xt (such a curiosity exists in substrate). Moreover, the transactions are ordered at the pool level according to round for which they provide a score.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have added tests
• I have made neccessary updates to the Infrastructure
• I have made corresponding changes to the existing documentation
• I have created new documentation
• I have bumped spec_version and transaction_version
• I have bumped aleph-client version if relevant