Add multi-database discovery and grouping features

This update introduces optional automatic discovery and onboarding of all databases on a PostgreSQL instance. It also enhances the frontend UI with grouped target display and navigation, making it easier to view and manage related databases. Additionally, new backend endpoints and logic ensure seamless integration of these features.

backend/app/schemas/target.py

@@ -16,6 +16,7 @@ class TargetBase(BaseModel):
 
 class TargetCreate(TargetBase):
     password: str
+    discover_all_databases: bool = False
 
 
 class TargetConnectionTestRequest(BaseModel):