feat: Add support for flyout menu mode in MegaMenu

- Introduced `MegaMenuMode` type and `normalizeMegaMenuMode` function to handle menu modes.
- Updated `MegaMenuApplicationCustomizer` to accept `menuMode` property.
- Enhanced `MegaMenuRenderer` to render flyout menus based on the selected mode.
- Created new HTML previews for both flyout and mega menu modes.
- Removed unused mock services and user custom action service interfaces.

config/package-solution.json

@@ -3,7 +3,7 @@
   "solution": {
     "name": "mega-menu-client-side-solution",
     "id": "f4660e06-ce08-43ee-bfb7-5c4464e01133",
-    "version": "2.0.1.0",
+    "version": "2.1.0.0",
     "includeClientSideAssets": true,
     "skipFeatureDeployment": true
   },