feat(extras): Add "Dismiss all" action to notifications dropdown

Introduce a view to allow users to dismiss all unread notifications with
a single action. Update the notifications' template to include a
"Dismiss all" button for enhanced usability. This addition streamlines
notification management and improves the user experience.

Fixes #20301

netbox/utilities/htmx.py

@@ -1,5 +1,11 @@
+from django.http import HttpResponse
+from django.urls import reverse
+from urllib.parse import urlsplit
+
 __all__ = (
+    'htmx_current_url',
     'htmx_partial',
+    'htmx_maybe_redirect_current_page',
 )
 
 
@@ -9,3 +15,45 @@ def htmx_partial(request):
     in response to an HTMX request, based on the target element.
     """
     return request.htmx and not request.htmx.boosted
+
+
+def htmx_current_url(request) -> str:
+    """
+    Extracts the current URL from the HTMX-specific headers in the given request object.
+
+    This function checks for the `HX-Current-URL` header in the request's headers
+    and `HTTP_HX_CURRENT_URL` in the META data of the request. It preferentially
+    chooses the value present in the `HX-Current-URL` header and falls back to the
+    `HTTP_HX_CURRENT_URL` META data if the former is unavailable. If neither value
+    exists, it returns an empty string.
+    """
+    return request.headers.get('HX-Current-URL') or request.META.get('HTTP_HX_CURRENT_URL', '') or ''
+
+
+def htmx_maybe_redirect_current_page(
+    request, url_name: str, *, preserve_query: bool = True, status: int = 200
+) -> HttpResponse | None:
+    """
+    Redirects the current page in an HTMX request if conditions are met.
+
+    This function checks whether a request is an HTMX partial request and if the
+    current URL matches the provided target URL. If the conditions are met, it
+    returns an HTTP response signaling a redirect to the provided or updated target
+    URL. Otherwise, it returns None.
+    """
+    if not htmx_partial(request):
+        return None
+
+    current = urlsplit(htmx_current_url(request))
+    target_path = reverse(url_name)  # will raise NoReverseMatch if misconfigured
+
+    if current.path.rstrip('/') != target_path.rstrip('/'):
+        return None
+
+    redirect_to = target_path
+    if preserve_query and current.query:
+        redirect_to = f'{target_path}?{current.query}'
+
+    resp = HttpResponse(status=status)
+    resp['HX-Redirect'] = redirect_to
+    return resp