Ensure everyone has a "key" in our list of people

[melange396]

Make sure there is an explicit and unique key for each person entry in https://github.com/cmu-delphi/www-main/blob/dev/content/people/index.md?plain=1 . If no "key" exists, the system seems to simply use the first name, which can easily cause collisions and confusion. This affected us and was dealt with in #974.

One way to accomplish this is to use people's "andrew" IDs which are already unique, though something creative will have to be done for people who do not have proper or sponsored andrew accounts.

If changing or adding a new key for someone, references will have to be updated. For example, if we change ryan to ryantibs, we must modify uses of the former.