FEATURE: Add modal for editing tags in navigation menu (#22214)

What does this change do?

This change is a first pass for adding a modal used to edit tags that appears in
the navigation menu. As the feature is being worked on in phases, it is
currently hidden behind the `new_edit_sidebar_categories_tags_interface_groups` site setting.

The following features will be worked on in future commits:

1. Input filter to filter through the tgas
2. Button to reset tag selection to default navigation menu tags site
   settings
3. Button to deselect all current selection

spec/system/page_objects/modals/sidebar_edit_tags.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module PageObjects
+  module Modals
+    class SidebarEditTags < PageObjects::Modals::Base
+      def closed?
+        has_no_css?(".sidebar-tags-form-modal")
+      end
+
+      def has_right_title?(title)
+        has_css?(".sidebar-tags-form-modal #discourse-modal-title", text: title)
+      end
+
+      def has_tag_checkboxes?(tags)
+        tag_names = tags.map(&:name)
+
+        has_css?(".sidebar-tags-form-modal .sidebar-tags-form__tag", count: tag_names.length) &&
+          all(".sidebar-tags-form-modal .sidebar-tags-form__tag").all? do |row|
+            tag_names.include?(row["data-tag-name"].to_s)
+          end
+      end
+
+      def toggle_tag_checkbox(tag)
+        find(
+          ".sidebar-tags-form-modal .sidebar-tags-form__tag[data-tag-name='#{tag.name}'] .sidebar-tags-form__input",
+        ).click
+
+        self
+      end
+
+      def save
+        find(".sidebar-tags-form-modal .sidebar-tags-form__save-button").click
+        self
+      end
+    end
+  end
+end