[FIX] website_slides: limit auto subscription

In order to avoid spam and unwanted notification this commit limits auto
subscription on channel when

 * creating a channel;
 * automatically telling a channel a new publication has been done;
 * creating a slide;

As being a follower of a slide channel means following its slides user should
choose manually to be follower of a channel, notably through the UI.

A new way of managing subscription will come with elearning in mind and
therefore auto subscription should be limited.

Commit linked to task ID 1933820 and PR #30830.

addons/website_slides/models/slide_channel.py

@@ -145,6 +145,10 @@ class Channel(models.Model):
         if self.visibility == 'public':
             self.group_ids = False
 
+    @api.model
+    def create(self, vals):
+        return super(Channel, self.with_context(mail_create_nosubscribe=True)).create(vals)
+
     @api.multi
     def write(self, vals):
         res = super(Channel, self).write(vals)

addons/website_slides/models/slide_slide.py

@@ -234,7 +234,6 @@ class Slide(models.Model):
         if not self.user_has_groups('website.group_website_publisher'):
             values['website_published'] = False
         slide = super(Slide, self).create(values)
-        slide.channel_id.message_subscribe(partner_ids=self.env.user.partner_id.ids)
         slide._post_publication()
         return slide
 
@@ -325,7 +324,7 @@ class Slide(models.Model):
             publish_template = slide.channel_id.publish_template_id
             html_body = publish_template.with_context(base_url=base_url)._render_template(publish_template.body_html, 'slide.slide', slide.id)
             subject = publish_template._render_template(publish_template.subject, 'slide.slide', slide.id)
-            slide.channel_id.message_post(
+            slide.channel_id.with_context(mail_create_nosubscribe=True).message_post(
                 subject=subject,
                 body=html_body,
                 subtype='website_slides.mt_channel_slide_published',