chore: Search optimisations (#6644)

- Strip search term before searching
- order messages by created_at desc
- order contacts by last_activity_at desc
- order conversations by created_at desc
- Search only resolved contacts
- Optimize resolved contacts query

ref: #6583

app/models/notification.rb

@@ -42,6 +42,8 @@ class Notification < ApplicationRecord
 
   after_create_commit :process_notification_delivery, :dispatch_create_event
 
+  # TODO: Get rid of default scope
+  # https://stackoverflow.com/a/1834250/939299
   default_scope { order(id: :desc) }
 
   PRIMARY_ACTORS = ['Conversation'].freeze