Fix missing URI for "OAuthServerClient" object handles, causing dialog with no button

Summary:
Ref T13330. Handles for "OAuthServerClient" objects currently do not have a URI, which causes some obscure fallout like a missing "Close" button when examining their transactions.

Add a URI.

Test Plan:

• Viewed an OAuth server client detail page.
• Edited a policy, changing it to a custom policy.
• Clicked "Custom Policy" in the resulting transaction to view a dialog explaining the changes.
• Before change: dialog has no close button.
• After change: dialog has a close button.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13330

Differential Revision: https://secure.phabricator.com/D20624