Fixes #21173: Fix plugin menu registration order timing issue (#21248)

* Fixes #21173: Fix plugin menu registration order timing issue

- Converted static MENUS list to dynamic get_menus() function
- Ensures plugin menus are built at request time after all plugins complete ready()
- Fixes issue where only first few plugin menus appeared in navigation sidebar
- Updated navigation template tag to call get_menus() dynamically

* Fix ruff linting errors

- Add missing blank line before get_menus() function definition
- Remove trailing whitespace

* Add @cache decorator to get_menus() for performance optimization

Per reviewer feedback, the menu list is now cached since it doesn't change
without a Django restart. This eliminates redundant list building on each request.

---------

Co-authored-by: adionit7 <adionit7@users.noreply.github.com>

netbox/utilities/templatetags/navigation.py

@@ -1,6 +1,6 @@
 from django import template
 
-from netbox.navigation.menu import MENUS
+from netbox.navigation.menu import get_menus
 
 __all__ = (
     'nav',
@@ -19,7 +19,7 @@ def nav(context):
     nav_items = []
 
     # Construct the navigation menu based upon the current user's permissions
-    for menu in MENUS:
+    for menu in get_menus():
         groups = []
         for group in menu.groups:
             items = []