Add ability to paste lists of names into Meeting Attendees

To work around #5905 I:
1) Opened a new mail
2) Put the DL I wanted to add in the To box and expanded it
3) Copied the resultant list of names
4) Pasted the list of names into the Meeting Attendees box. (It was about 15 names.)

This sadly does not work. After sitting for a time it showed me this error:
```
SearchUsers.Run failed: { "error": { "code": 504, "source": "redacted", "clientRequestId": "redacted", "message": "BadGateway", "innerError": { "error": { "code": "ResponseTimeout", "message": "The server did not receive a timely response from the upstream server. Request tracking id 'redacted'." } } } }
```

Start by reproducing the listed steps in Meeting Attendees with a pasted list of names, then trace the SearchUsers.Run request that fails with a timeout. Done means pasted attendee lists are accepted and processed without the reported timeout error; the payload names no files or tests to run.

Written by the indexing model from the issue text.