AMM: Implement the indexer

[Braqzen]

Indexer Guideline

The AMM consists of two contracts therefore we can separate the indexer into two modules.

Each index should contain functions in the format index_<event_name>.

E.g.

#[indexer(manifest = "<path/to/file/amm.manifest.yaml>")]
mod amm_index {
    fn index_register_pool_event(event: RegisterPoolEvent, block: BlockData) { ... }
}

#[indexer(manifest = "<path/to/file/amm-exchange.manifest.yaml>")]
mod amm_exchange_index {
    fn index_add_liquidity_event(event: AddLiquidityEvent, block: BlockData) { ... }

   // more events
}

Each type in graphql should have a required field.

Certain event fields would benefit from the @indexed directive.

• AMM
  • RegisterPoolEvent
    • asset_pair
    • pool
• Exchange
  • AddLiquidityEvent
    • added_assets
  • DepositEvent
    • deposited_asset
  • RemoveLiquidityEvent
    • removed_reserve
  • SwapEvent
    • input
    • output
  • WithdrawEvent
    • withdrawn_asset

From the BlockData we should retrieve the block height and add it to each event so that we have a measure of time for when the event took place.

[bitzoic]

Closing in favor of #605