chore (postgres): Make nwaku to reconnect to the Postgres database if it restarts

[Ivansete-status]

Background

Postgres is one of the data sources used when a nwaku node has the store protocol mounted. The connection between nwaku & postgres should be established if both processes are running.

Details

During manual testing, I realized that if the Postgres database is restarted manually, then the nwaku doesn't try to establish a connection again. Therefore, nwaku should retry to connect in case the connection is interrupted.

Acceptance criteria

The nwaku can properly establish a connection if the Postgres database is restarted many times and no leak happens after thousand of Postgres restarts.

[vpavlin]

This has other implications - what if nwaku tries to reconnect, but it can?

I can see 2 outcomes - it either "unmounts" store protocol (as it is unusable at that point), but that is kinds counter intuitive for the operator as the node seems completely healthy, it "just" degraded it's services

Or we "kill" the node if it cannot reconnect - then it is obvious for the operator that there is something to fix