Revert "refactor: Consolidate dbproxy and user models (#461)"

[dmohns]

This reverts commit 00d566a06bd9f57dbe624b579a1be28ff5c7fcab.

Brief summary of the change made

Closes: #592

Currently, the Agent login is broken. And I'm not so sure anymore there is even a way to fix it.

This is how the model used to work before your change. Essentially both User and Agent models live in Tenant space. Then a Pivot table (DatabaseProxy) is used to map both of them to the corresponding Tenants.

In the updated model, there is no way (no pivot table) to map Agents to Tenants 🙀 . The only way would be to also make every Agent a User. But I don't think we can do this.
Because

Both Agents and Users have the Authenticatable trait. I.e. Agents could then log in as Users, but we don't want that. (specifically because we don't have a fully working Role/Permissions model)
Both Agent and User tables maintain password fields. We would either have to keep them in sync or change the Auth governance. Both of which seem to introduce more complexity than they remove.

Are there any other side effects of this change that we should be aware of?

Describe how you tested your changes?

Pull Request checklist

Please confirm you have completed any of the necessary steps below.

• Meaningful Pull Request title and description
• Changes tested as described above
• Added appropriate documentation for the change.
• Created GitHub issues for any relevant followup/future enhancements if appropriate.