Warn instructors when creating LMS URL assignments that point to a google doc

**The problem**

Google Docs can be made using publicly-available URLs, and users creating LMS assignments may not understand that the nature of Docs' use of frames won't be compatible with Hypothesis. Since we know this sort of link won't work (as opposed to, for example, a Doc that's been published to the web), we might warn instructors who are making those assignments that Hypothesis may not work as expected with that URL.

**The solution**

Look for LMS app assignments using URLs like https://docs.google.com/document/d/.... and warn instructors that this URL may not work properly in Hypothesis. A confirmation step before continuing could let them still continue if they choose to, also giving them a chance to change the URL before saving the assignment.

The published to the web documents seem to look like https://docs.google.com/document/d/e/.../pub.

The end result might be a blocklist and an allowlist of URLs with wildcards, where the blocklist shows a warning and confirmation step to instructors before letting them continue.

Start by reviewing the LMS app assignment-creation flow and how it handles submitted URLs. Define the Google Docs URL patterns that should warn, include an option to continue or change the URL, and verify that published-to-the-web URLs are handled appropriately.

Written by the indexing model from the issue text.