Permit attachments in mailbox conductor params

Prior to this commit, when adding attachments to an inbound email
through the conductor, the log would warn of an unpermitted parameter
with the message:

> Unpermitted parameter: :attachments. Context: { }

Also, if an application had the setting:

  config.action_controller.action_on_unpermitted_parameters = :raise

it would raise an error, because the attachments are not a permitted
parameter.

This commit also sets `action_on_unpermitted_parameters` to `:raise`
for the action mailbox test suite, so that tests are run in most
restrictive setting available, to prevent future unpermitted parameters
from being passed by conductor actions.

Co-authored-by: Dana Henke <danapalazzo1@gmail.com>

actionmailbox/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   Add `attachments` to the list of permitted parameters for inbound emails conductor.
+
+    When using the conductor to test inbound emails with attachments, this prevents an
+    unpermitted parameter warning in default configurations, and prevents errors for
+    applications that set:
+
+    ```ruby
+    config.action_controller.action_on_unpermitted_parameters = :raise
+    ```
+
+    *David Jones*, *Dana Henke*
+
 *   Add ability to configure ActiveStorage service
     for storing email raw source.
 

actionmailbox/app/controllers/rails/conductor/action_mailbox/inbound_emails_controller.rb

@@ -20,14 +20,18 @@ module Rails
 
     private
       def new_mail
-        Mail.new(params.require(:mail).permit(:from, :to, :cc, :bcc, :x_original_to, :in_reply_to, :subject, :body).to_h).tap do |mail|
+        Mail.new(mail_params.except(:attachments).to_h).tap do |mail|
           mail[:bcc]&.include_in_headers = true
-          params[:mail][:attachments].to_a.each do |attachment|
+          mail_params[:attachments].to_a.each do |attachment|
             mail.add_file(filename: attachment.original_filename, content: attachment.read)
           end
         end
       end
 
+      def mail_params
+        params.require(:mail).permit(:from, :to, :cc, :bcc, :x_original_to, :in_reply_to, :subject, :body, attachments: [])
+      end
+
       def create_inbound_email(mail)
         ActionMailbox::InboundEmail.create_and_extract_message_id!(mail.to_s)
       end

actionmailbox/test/dummy/config/environments/test.rb

@@ -46,4 +46,7 @@ Rails.application.configure do
 
   # Annotate rendered view with file names
   # config.action_view.annotate_rendered_view_with_filenames = true
+
+  # Raise error if unpermitted parameters are sent
+  config.action_controller.action_on_unpermitted_parameters = :raise
 end