Move away from prisma v1 for node-watcher.

[Tbaut]

Prisma 1 is accumulating security vulnerabilities, without any proper path for migration to v2 (subscriptions not available and not planned for the near future cf prisma/prisma#298).

The harvester should move to hasura, this also removes the need for open-server.
An alternative, because SQL is now supported by hasura, there could be a hasura on top of a SQL DB (built by the python lib from Polkascan?).

[Tbaut]

Although we have experience with hasura, I just saw that Polkastat has such a back-end that we can get inspired by https://github.com/Colm3na/polkastats-backend-v3