Navbar customization improvements (#17863)

- Add folder icon editing support
- And other navbar customization fixes/improvements.

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Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>
Co-authored-by: Devessier <baptiste@devessier.fr>
Co-authored-by: Félix Malfait <felix.malfait@gmail.com>

packages/twenty-shared/src/application/navigationMenuItemManifestType.ts

@@ -2,6 +2,7 @@ import { type SyncableEntityOptions } from '@/application/syncableEntityOptionsT
 
 export type NavigationMenuItemManifest = SyncableEntityOptions & {
   name?: string;
+  icon?: string;
   position: number;
   viewUniversalIdentifier?: string;
   link?: string;