Document - External is missing workbench access setting

[kevwalsh]

Describe the defect
"Document - External" media does not respect workbench access.

To Reproduce
Steps to reproduce the behavior:

1. As any content_editor, you can currently edit any "Document - External" media.

Expected behavior

Content editors should only be able to edit "Document - External" media that are in their section

Implementation

1. Go to admin/config/workflow/workbench_access/access_scheme/section/edit
2. Check "Document - External"
3. Save and export config.

Screenshots

Desktop (please complete the following information if relevant, or delete):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here. Reach out to the Product Managers to determine if it should be escalated as critical (prevents users from accomplishing their work with no known workaround and needs to be addressed within 2 business days).