Use Chaingraph for Subscriptions

[mr-zwets]

Currently the server uses subscriptions to an electrum server, ideally this would use subscriptions to the chaingraph server so only one indexer is used to get the state of the blockchain.

// Listen for notifications and set up a subscription with callback function.
electrum.on('notification', () => updateMintingUtxos());
await electrum.subscribe('blockchain.address.subscribe', contractAddressMint);

Streaming subscriptions are only available using chaingraph with an updated Hasura dependency >v2.7.
This way updateMintingUtxos could be removed as we can only change the minting utxo which changed.

more info: https://hasura.io/docs/latest/subscriptions/postgres/index/

possible graphql subscription library to use: https://github.com/nearform/graphql-hooks