feat(consenus):[CON-1565] splitting cup share making/validating/aggregating

[kpop-dfinity]

During subnet splitting, when replicas detect that

Implement the logic of subnet splitting CUP share creation, validation, and aggregation.

CUP shares creation

When a replica detects that a "subnet splitting" block (denoted by a new field, subnet-splitting-status in the DkgSummary struct) has been finalized and the state at the block's height has been committed, it will create a CUP in the following way:

1. Create a new summary block, on the fly, at the next CUP height, with dkg transcript taken from the registry;
2. Create a dummy random beacon at the next CUP height,
3. Check if node belongs to the high threshold committee, based on the transcript from the newly created summary block, if not, return None,
4. Create a CUP, with the block and random beacon created in steps 1. and 2., respectively, and sign it using the key material from the block.

CUP shares validation

CUP shares aggregation