chore: initial statistics subsystem

[EclesioMeloJunior]

Description

• Creates Statistics Collector subsytem
• Defines the subsystem messages

/// Messages sent to the Statistics Collector subsystem.
#[derive(Debug)]
pub enum StatisticsCollectorMessage {
	// Approval vote received
	ApprovalVoting(Hash, CandidateHash, (ValidatorIndex, DelayTranche)),

	// Candidate received enough approval and now is approved
	CandidateApproved(CandidateHash, Hash),

	// Set of candidates that has not shared votes in time
	ObservedNoShows(SessionIndex, Vec<ValidatorIndex>),

	// All relay block's candidates are approved, therefore relay block is approved
	RelayBlockApproved(Hash)
}

• Updated approval-voting to send data to the statistics collector subsytem

---

Next Steps

• Collect approval distribution metrics (upload & downloads)
  • Define subsystem messages
  • Update approval distribution to send messages
• Publish prometheus metrics
• Calculate approvals tallies

[CLAassistant]

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1 out of 2 committers have signed the CLA.

✅ EclesioMeloJunior
❌ EgorPopelyaev
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