feat: Ability to block contacts permanently (#8922)

Co-authored-by: Pranav <pranav@chatwoot.com>

db/migrate/20240213131252_add_blocked_to_contacts.rb

@@ -0,0 +1,6 @@
+class AddBlockedToContacts < ActiveRecord::Migration[7.0]
+  def change
+    add_column :contacts, :blocked, :boolean, default: false, null: false
+    add_index :contacts, :blocked
+  end
+end