Added automatic nightly SQLite backups

Resolves #22

spoolman/api/v1/models.py

@@ -159,3 +159,12 @@ class Spool(BaseModel):
 
 class HealthCheck(BaseModel):
     status: str = Field(example="healthy")
+
+
+class BackupResponse(BaseModel):
+    success: bool = Field(description="Whether the backup was created successfully.", example=True)
+    path: Optional[str] = Field(
+        default=None,
+        description="Path to the created backup file.",
+        example="/home/app/.local/share/spoolman/backups/spoolman.db",
+    )