[Package Renames] Add message for pending popularity transfers on "Manage Package" page

[loic-sharma]

Popularity transfer may take over an hour to propagate to search. The customers should see an alert on the "Manage Package" page that the popularity transfers are pending.

Depends on:

• NuGetGallery#7908 - Add Package Renames form to "Manage Package" page
• NuGetGallery#7903 - Expose popularity transfers in search

The work to "speed up" popularity transfers is tracked by: #7911

[loic-sharma]

Closing as per #7896 (comment)