Migrate to Datasource instead of DriverManager

[kcinay055679]

Right now we use DriverManager as a way to get the DB connection, but it is recommended to use Datasource.
More information:
https://stackoverflow.com/questions/15198319/why-do-we-use-a-datasource-instead-of-a-drivermanager

Describe the solution you'd like
I would like to use Datasouroce since it is the best practice to interact with the db

This guide should help:
https://www.baeldung.com/multitenancy-with-spring-data-jpa#bd-dynamic-datasource-routing
But keep in mind this guide is written for Database per Tenant: while we use schema per tenant therefore we have to make a few adjustments