Override Hyrax mailer to inject tenant ID into contact form submissions

Fixes #1230

app/mailers/hyrax/contact_mailer.rb

@@ -0,0 +1,19 @@
+module Hyrax
+  # Mailer for contacting the administrator
+  class ContactMailer < HykuMailer
+    def contact(contact_form)
+      @contact_form = contact_form
+      # Check for spam
+      return if @contact_form.spam?
+      headers = @contact_form.headers.dup
+      headers[:subject] << " [#{current_tenant_id}]"
+      mail(headers)
+    end
+
+    private
+
+      def current_tenant_id
+        Account.find_by(tenant: Apartment::Tenant.current)&.cname || Account.admin_host
+      end
+  end
+end