refactor: allow digitalocean custom DB users and names

Description

This MR adds the ability of defining custom user and database names for both MySQL and MongoDB on DigitalOCean and AWS.

Supporting information

https://tasks.opencraft.com/browse/SE-5927

Testing instructions

Steps to test the changes:

1. Check that pipeline succeeds: https://gitlab.com/opencraft/ops/grove-stage-aws/-/pipelines/852719302

Dependencies

There is a pending fix this MR depends on, fixing timeouts and smaller Grove issues.

Screenshots

N/A

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated

Additional context

We are not allowing password overrides for multiple reasons. One of the many reasons is the additional complexity that would bring in. If someone wants to define custom names to migrate an existing instance to Grove, a possible solution to lack of password override can be:

• Import database
• Apply user related terraform plan

That way, a new user will be created with the necessary permissions for the existing database without username conflicts and database (name) duplicaiton.