Add holiday management functionality with CRUD operations

- Implement HolidaysController for managing holidays
- Create Holiday model with validation for recurrence types
- Add holiday form and views for creating, editing, and listing holidays
- Integrate holiday checks into customer appointment scheduling
- Update locale file for holiday-related labels and error messages
- Add migration for holidays table
- Update plugin version and add holidays to admin menu

app/views/holidays/new.html.erb

@@ -0,0 +1,7 @@
+<h2><%= l(:label_holiday_new, default: 'New Holiday') %></h2>
+
+<%= form_with model: @holiday, url: holidays_path, local: true do |f| %>
+  <%= render partial: 'form', locals: { f: f } %>
+  <%= submit_tag l(:button_create) %>
+  <%= link_to l(:button_cancel), holidays_path, class: 'cancel' %>
+<% end %>