allow passing custom connection instance to the connectors

[Hebilicious]

Describe the feature

Db0 scope seems to be to provide a connector for every SQL-like language out there, as well as a wrapper around popular ORM. I think we should consider letting the user initialise the client however he see fits, and pass the client instance to the connector. If we do provide every single client, we endup having to manage and take care of many depedencies that we do not control, and we run into the problems where someone want to use the client without db0 and has to create two of them, or we have to expose the client etc

We could document how to install and initialise the client for each connector.

Additional information

• [ ] Would you be willing to help implement this feature?