Separate the pipeline events into block and transaction events

[DCNick3]

Also consider switching the block events filtering to use height, as there's no real way to predict block hashes.

---

    // IMO it should have the suffix `Box`
    pub enum PipelineEventBox {
        Block(BlockEvent),
        Transaction(TransactionEvent),
    }

    struct BlockEvent {
        pub status: BlockStatus,
        // NOTE: Does it make sense to have hash filtering for blocks?
        // because it's unpredictable which block will be constructed
        // It might be only relevant when replaying blocks in which case we can use height
        // pub hash: HashOf<SignedBlock>,
        pub height: u64,
    }

    struct TransactionEvent {
        pub status: TransactionStatus,
        pub hash: HashOf<SignedTransaction>,
    }

    // FIXME: Some variants are never actually emitted. Fix this in the codebase
    enum BlockStatus {
        Validating,
        Committed,
        Rejected(crate::block::error::BlockRejectionReason),
    }

    // FIXME: Some variants are never actually emitted. Fix this in the codebase
    enum TransactionStatus {
        Validating,
         // it's factually incorrect to say that transaction was committed unless block get committed
        Approved,
        // Rejected transactions are also committed
        Rejected(crate::transaction::error::TransactionRejectionReason),
        // I think we can emit a batch of committed transaction events at the time of block commit
        Committed,
    }

I think this makes more sense

Originally posted by @mversic in https://github.com/hyperledger/iroha/pull/4240#discussion_r1497192564