Function init 

pub async fn init<ReadStateService, Tip>(
    listen_addr: SocketAddr,
    read_state: ReadStateService,
    chain_tip_change: Tip,
    mempool_change: MempoolTxSubscriber,
) -> Result<(JoinHandle<Result<(), BoxError>>, SocketAddr), BoxError>
where
    ReadStateService: ReadState,
    Tip: ChainTip + Clone + Send + Sync + 'static,

Initializes the indexer RPC server