[TASK] Event watcher for relayer

[salman01zp]

Overview

Add event watcher for relayer which will watch for the Vanchor deposit event and create lc-proposal and send them to pallet light-proposal-handler

/// Light Client Proposal.
///
/// On Vanchor deposit event the [`LightClientProposal`] sends a light storage proofs along with block headers to tangle
///  Tangle verifies this storage proofs and creates Anchor update proposals for each connected chains
/// The format of the proposal is:
/// ```text
/// ┌────────────────────┬─────────────────┬─────────────────────┐
/// │                    │                 │                     │
/// │    BlockHeader     │  Storage proof  │    Storage proof    │
/// │                    │     Root        │      Leaf Index      │
/// └────────────────────┴─────────────────┴─────────────────────┘
/// ```
#[derive(Proposal, Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub struct LightProposal {
    block_header: BlockHeader,
    merkle_root_proof: Vec<u8>,
    leaf_idx_proof: Vec<u8>,
}

Task Checklist

• Event watcher for deposit event (featured-flag)
• Query Tangle to see when the block header has been relayed.
• Fetch storage proofs for merkle-root and leaf-idx
• Construct BlockHeader
• Construct LightProposal and send to pallet light-proposal-handler