Upgrade to @apollo/client v3

[djmitche]

We currently use react-apollo. which was deprecated in favor of @apollo/client. This will require figuring out what needs to change to use that version of @apollo/client. The breaking changes appear to be listed here.

[djmitche]

I got a start here -- https://github.com/mozilla-frontend-infra/codetribute/compare/master...djmitche:issue420?expand=1

The tricky bit seems to be that the fragment matcher will need to be rewritten - https://www.apollographql.com/docs/react/data/fragments/#defining-possibletypes-manually

I don't know much about apollo, so if someone knows how to do this quickly, please take over! :)

[djmitche]

I've got some more work at the link above. I think I got the possibleTypes defined correctly, and I think I found all of the imports. But now it crashes Firefox in some kind of infinite loop.

I'm going to give up on this. Not that it's impossible, but it probably needs someone who's familiar with how apollo 3.0 works.