feat: Add a placeholder for image attachments in conversations view (#8969)

We analyze an image to get it's height and width. On the frontend, we would show a placeholder with the corresponding width and height until the images are loaded properly.

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Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

app/models/attachment.rb

@@ -76,7 +76,9 @@ class Attachment < ApplicationRecord
       extension: extension,
       data_url: file_url,
       thumb_url: thumb_url,
-      file_size: file.byte_size
+      file_size: file.byte_size,
+      width: file.metadata[:width],
+      height: file.metadata[:height]
     }
 
     metadata[:data_url] = metadata[:thumb_url] = external_url if message.instagram_story_mention?