[IMP] website_slides: add a setting to install website_sale

Purpose
=======

With the new 'website_slides_sale' module users can now sell slide.channels.

This commit adds a setting to let the user know he has to install website_sale
to be able to sell courses / documentation.

addons/website_slides/models/res_config_settings.py

@@ -1,10 +1,11 @@
 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
-from odoo import api, fields, models
+from odoo import fields, models
 
 
 class ResConfigSettings(models.TransientModel):
     _inherit = "res.config.settings"
 
     website_slide_google_app_key = fields.Char(related='website_id.website_slide_google_app_key', readonly=False)
+    module_website_sale_slides = fields.Boolean("Sell courses")

addons/website_slides/views/res_config_settings_views.xml

@@ -26,6 +26,18 @@
                         </div>
                     </div>
                 </div>
+                <div class="col-12 col-lg-6"></div>
+                <div class="col-12 col-lg-6 o_setting_box" id="slides_install_website_sale">
+                    <div class="o_setting_left_pane">
+                        <field name="module_website_sale_slides"/>
+                    </div>
+                    <div class="o_setting_right_pane">
+                        <label for="module_website_sale_slides"/>
+                        <div class="text-muted">
+                            Sell courses on your website
+                        </div>
+                    </div>
+                </div>
             </div>
         </field>
     </record>