## Description 

This PR is:
* abstracting via a guard the acquisition of locking, metric reporting &
logging when start/shutdown the consensus engines to be used by the
managers
* implementing the start/shutdown methods for the MysticetiManager to
start/shutdown the mysticeti validator. Necessary type conversations
take place. Some assumptions have been made for now for the integration
reasons (some TODOs have been left)
* a simple test has been added for the MysticetiManager - will add more
cases on follow up PRs

**Note:** a few types on Mysticeti had to be opened up to allow
initialising and pass them to the mysticeti validator. PR here
https://github.com/MystenLabs/mysticeti/pull/36

Next steps
- [ ] Wire in to Mysticeti Validator the `ConsensusHandler`
- [ ] Wire in to Mysticeti Validator the TxValidator
- [ ] Introduce property to flip between Narwhal & Mysticeti and allow
initialising Mysticeti as consensus engine
- [ ] Adapt MysticetiManager to wire in or return the component to
communicate with the Mysticeti validator and submit transactions

## Test Plan 

CI

---
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### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes