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/serve.json

@@ -10,7 +10,9 @@
           "location": "ClientSideExtension.ApplicationCustomizer",
           "properties": {
             "termSetName": "Horizontale Navigation",
-            "additionalCssUrl": "/siteAssets/Navigation/Navigation.css"
+            "cacheMinutes": 15,
+            "menuMode": "megaMenu",
+            "debug": true
           }
         }
       }
@@ -21,7 +23,10 @@
         "c0abbffb-355d-4d4e-bd38-9e15fb811506": {
           "location": "ClientSideExtension.ApplicationCustomizer",
           "properties": {
-            "testMessage": "Test message"
+            "termSetName": "Global Navigation",
+            "cacheMinutes": 15,
+            "menuMode": "flyout",
+            "debug": true
           }
         }
       }