Links to attachments are broken after a migration

Issue Summary

If you have hardcoded links to attachments and you migrate over to the Cloud those links will be broken.

Steps to Reproduce

1. Insert an attachment on a page.
2. On the sidebar of the page, click on the three-dotted button select "Attachments" from the menu.
3. Copy the link, it should be something like this for Cloud https://instance.atlassian.net/wiki/download/attachments/pageid/attachment_name?api=v2
4. Paste on another page

Expected Results

Links would be updated to the new URL and the page id's as well.

Actual Results

The links will be broken still pointing to the old instance.

Workaround

We don't have a fix for these links yet.

Note: This behavior currently affects any kind of Confluence migrations, site import, space import, and Cloud Migration Assistant. Since the page id's change, it's very difficult to map those to the new pages.