[SERF-3387] Support Multi DB connections

[Neurostep]

Description

In this PR we extend database.Config to support multi-DB connections.

This is a reference implementation using dbresolver gorm plugin. It covers all of the needs:

• Support several sources to be able to connect to different DBs and choose between DBs dynamically
• Support primary / replica configurations

This reference PR does not implement the connection pooling per primary/replica which can be done by extending this PR to cover that (actual implementation).

NOTE: this PR is not meant to be merged at this stage and has only a demo purpose.

Testing considerations

Checklist

• Prefixed the PR title with the JIRA ticket code
• Performed simple, atomic commits with good commit messages
• Verified that the commit history is linear and commits are squashed as necessary
• Thoroughly tested the changes in development and/or staging
• Updated the README.md as necessary

Related links

• https://gorm.io/docs/dbresolver.html
• SERF-3387