Fix Rails 7 Regression - ActiveStorage Content Disposition

[alxjrvs]

Summary

When upgrading our app from 6.1.4.1 to 7, we noticed that the following code no longer functioned:

class Settings::My::StaffUploadsController < Settings::MyController

  # GET /1/settings/my/downloads/staff_uploads/1
  def show
    @staff_upload = Current.user.staff_uploads.active.find(params[:id])

    redirect_to rails_blob_path(@staff_upload.file, disposition: :attachment)
  end
end

Originally, this worked as expected, redirecting the file and triggering the browser to download it as an attachment. After the upgrade, it redirected to the attachment, but the disposition was always inline.

Root Cause

After a brief investigation, I determined that this regression was introduced in ab8e3d22 where @dhh refactored/simplifed the ActiveStorage ProxyController code, but forgot to pass the disposition parameter into the callers of his newly created method ( send_blob_stream).

Resolution

This PR passes the missing option to the Blob:ProxyController and the Representations:ProxyController's send_blob_stream call, and added tests to ensure these do not regress in the future.

We are using this solution locally in our Rails 7 Upgrade to great effect.