fix(extensions): show error when toggle fails

[debsmita1]

Hey, I just made a Pull Request!

Resolves:
https://issues.redhat.com/browse/RHDHBUGS-2125

When the dynamic-plugins yaml file configured in the extensions configuration is incorrect, the toggle action fails due to "FILE_NOT_EXISTS" err. The network call fails, but the err is not displayed in the UI. This gives the impression that the toggle button doesn't work.

As part of this PR

• If the toggle fails for any reason, it is displayed in the UI via a Snackbar Alert
• but for the 'Download YAML` action, if the configured file is incorrect, we let the user download a minimal version of the plugin, which would look like

- package: ../<package-path>
  disabled: false

Along with an info in the browser's console saying No configuration found for package <package-name>, downloaded a minimal YAML

Currently, whether the configured file exists or not is evaluated only when the package/plugin configuration is fetched. Because of this, the UI cannot determine the file’s existence beforehand

cc @dzemanov

GIF:

Screen.Recording.2026-01-22.at.12.44.41.PM.mov

Test setup:

In your extensions configuration, configure a file that doesn't exist

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or Updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)

[rhdh-gh-app]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@red-hat-developer-hub/backstage-plugin-extensions	workspaces/extensions/plugins/extensions	patch	v0.14.2

[sonarqubecloud]

Quality Gate passed

Issues
5 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ShiranHi]

@debsmita1 , thank you for this PR, I have one question:
To improve the user experience, could we disable the toggle when the configuration file is missing?
I suggest adding a tooltip on hover that explains: "The plugin cannot be disabled because the required dynamics-plugin.yaml file is missing." Additionally, we could provide a "Configure plugin" button that directs users to the configuration page where they can follow the instructions in the information bar. What do you think?