Preview link on CMS front end does not account for permalink override

[jhung]

Describe the bug

When using the CMS front end to create a new Page, the preview link is incorrect if a permalink is specified.

To Reproduce

Steps to reproduce the behavior:

1. Go to the IDRC site admin and create a new Page.
2. Give it a title (i.e. 'Intelligent User Interfaces for Virtual Healthcare').
3. In the Permalink field, enter a value (i.e. '/reducing-healthcare-barriers/').
4. Publish
5. Select the 'View Live' link - notice the 404 not found error.

Expected behavior

If a permalink is specified, the preview link should use that URL and not give a 404.

Screenshots

Preview seen using the "View Preview" link from the Netlify CMS front end:

Preview as seen from Github deploy preview. Notice the difference in URL: