Add QuorumDriver

[lxfind]

This PR adds a new component called QuorumDriver.
It provides 3 interface functions:

1. execute_transaction. This API takes a transaction and tries to execute it through the authority aggregator. It accepts 3 different request types, one returns immediately, one waits for the cert and one waits for the effects cert. In the first two cases, it schedules the transaction execution by sending a task to an event queue, which would be processed by an event processor.
2. next_effects. This allows a node to subscribe effects certs coming out of the quorum driver. A fullnode may want this ti get certs faster than waiting from validators.
3. update_validators. This can be called at epoch boundaries, when the committee and validator set changes.

[mystenmark]

This is a bit misleadingly named, isn't it? The TransactionEffects here is unsigned, so the client can't use this as a proof of finality. An effects cert would actually be a TransactionEffectsEnvelope<AuthorityQuorumSignInfo>, right?

FWIW I may look at forming effects certificates in full node, since I'm already going to be doing the work of waiting for finality before syncing a cert. I say "may" because fullnode can get away with merely proving finality to itself by observed 2f+1 idential effects digests - forming an fx cert involves further fetching 2f+1 signed effects.

[lxfind]

The plan here is to make it return TransactionEffectsEnvelope eventually.
Currently since authority_aggregator only returns effects, here I am leaving it as it is. I plan to send future PRs to actually make authority_aggregator return effects certs.

[mystenmark]

Evan built a very similar pattern for sending commands over a channel for lock_service.rs, I wonder if its worth abstracting that mechanism so we don't keep re-inventing it.

[patrickkuo]

objects.json, owned_objects.json and transactions.json doesn't have real changes, all changes are due to random ids and transaction hash, we can revert the changes.

[lxfind]

Address all feedback:

• Rebase
• Remove all mutex
• Added comments/clarifications on some items

[patrickkuo]

LGTM!