feat: Add unread badge to sidebar for inbox view (#10803)

# Pull Request Template

## Description

This PR adds a badge to the icon in the sidebar group header and an
unread highlight for the inbox view.

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

**Loom video**

https://www.loom.com/share/1a880aa16de249a1836b8d014325c067?sid=87cc7b64-667b-4066-8993-d33abccf7b67


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/store/modules/specs/notifications/getters.spec.js

@@ -95,4 +95,27 @@ describe('#getters', () => {
       state.notificationFilters
     );
   });
+
+  describe('getHasUnreadNotifications', () => {
+    it('should return true when there are unread notifications', () => {
+      const state = {
+        meta: { unreadCount: 5 },
+      };
+      expect(getters.getHasUnreadNotifications(state)).toBe(true);
+    });
+
+    it('should return false when there are no unread notifications', () => {
+      const state = {
+        meta: { unreadCount: 0 },
+      };
+      expect(getters.getHasUnreadNotifications(state)).toBe(false);
+    });
+
+    it('should return false when meta is empty', () => {
+      const state = {
+        meta: {},
+      };
+      expect(getters.getHasUnreadNotifications(state)).toBe(false);
+    });
+  });
 });