Issue Summary

When the customer has chosen plain text format for their notifications, the links to attachments in the notification contains links to internal Jira rather than the Customer portal

This is reproducible on Data Center: Yes

Steps to Reproduce

1. Install a vanilla instance of Jira Service Management.
   This was validated on JSM DC 5.13.1, 5.12.8, 5.15.2.
2. Go to System >> Default user preferences and update the 'Email format' to 'Text'
3. Set up the Outgoing email configuration to receive emails
4. Create a JSM project with sample data
5. Open one of the tickets and update the reporter to receive the emails
6. Now, add a comment to the ticket with an attachment and click on 'share with the customer'

Expected Results

The customer notification received by the reporter will not have any links to the internal Jira.

Actual Results

The customer notification has the attachment link which is referring to internal Jira rather than the customer portal as shown in the screenshot -

This is not affecting the 'view request'/'Turn off this request's notifications' links.

Workaround

The email format can be set back to 'HTML' from System >> Default user preferences >> Email format.