feat: Make devtools a feature

Users can now enable DevTools easily,
without worrying about forgetting 'uncomment' that function.

src-tauri/Cargo.toml

@@ -28,3 +28,5 @@ default = [ "custom-protocol" ]
 # this feature is used used for production builds where `devPath` points to the filesystem
 # DO NOT remove this
 custom-protocol = [ "tauri/custom-protocol" ]
+# Enable DevTools for debugging.
+devtools = []