[FEATURE] Add Update Available Notification for AKS Desktop

## Feature Summary

Add an in-app update notification experience to AKS Desktop that informs users when a newer version of the application is available. This feature should align with the existing Headlamp update notification experience and provide users with a clear and unobtrusive way to discover available updates.

## Motivation

AKS desktop download numbers seem to suggest that users are continuing to use older versions of the application without realizing newer releases are available. This can result in users missing important bug fixes, security updates, performance improvements, and new capabilities.

Today, Headlamp notifies users when an update is available, but AKS Desktop does not provide an equivalent experience. As AKS Desktop continues to add new features and improvements, users should be made aware when updates are available so they can stay current with the latest release.

## Detailed Description

Implement an update notification mechanism within AKS Desktop that periodically checks whether a newer release is available.
 
When a newer version is detected:
 
- Display a notification or modal informing the user that an update is available.
- Show the currently installed version and the available version.
- Provide a clear action to learn more or download the latest release.
- Allow users to dismiss the notification and continue working.
- Ensure the notification is presented in a way that does not interrupt critical workflows.
 
The experience should be consistent with the existing Headlamp update notification functionality where appropriate.

## Alternatives Considered

### Rely on release notes and external announcements
Users would need to regularly monitor GitHub releases, documentation, or community announcements for updates. This creates unnecessary friction and reduces visibility of new releases.

### Manual version checks
If the user downloaded the package from github, they would have to check github release page and download and install. If using Homebrew, the user can run the brew upgrade command, but there isn't a proactive mechanism that would make the user aware of the update. A similar scenario as Homebrew for Winget.

### Automatic updates
Automatically downloading and installing updates could provide a streamlined experience, but introduces additional security, compliance, and operational considerations. This proposal focuses only on update awareness and notification.

## Use Cases

1. As an AKS Desktop user, I want to be notified when a new version is available so that I can benefit from the latest features, fixes, and improvements.
2. When a new AKS Desktop release is published, I need an in-app notification so that I do not have to manually check for updates.
3. As an administrator testing preview capabilities, I want visibility into newer releases so that I can evaluate updates as they become available.
4. When running an older version of AKS Desktop, I need a clear indication that a newer version exists so that I can decide when to upgrade.

## Implementation Ideas

- Reuse or adapt the existing Headlamp update notification implementation.

## Additional Context

Headlamp already includes an update notification experience that informs users when a new version is available. The goal of this work is to provide a similar capability within AKS Desktop and maintain a consistent experience across both products.

This feature only covers notifying users that an update exists. Automatic download and installation of updates are out of scope.

## Acceptance Criteria

- [ ] AKS Desktop can determine whether a newer version is available.
- [ ] Users receive an in-app notification when a newer version is detected.
- [ ] Notification displays both the current version and available version.
- [ ] Users can dismiss the notification without blocking their workflow.
- [ ] Users are provided a link or action to obtain the latest release.
- [ ] The experience is consistent with the existing Headlamp update notification behavior where applicable.
- [ ] No notification is displayed when the user is already running the latest version.

## Checklist

- [ ] I have searched for existing feature requests
- [ ] I have provided clear use cases
- [ ] I have considered alternatives
- [ ] This feature aligns with the project's goals