Migrate to apollo server v4

[magicmark]

👋 thanks for this project! looks like we're still using apollo server v3 - making a tracking ticket to update to v4.

Providing this stack trace so it hopefully shows up for folks googling it:

Unexpected error processing request: TypeError: Cannot read property 'getSpanByPath' of undefined

  at internalExecuteOperation (node_modules/@apollo/server/src/ApolloServer.ts:1304:19)
  at runHttpQuery (node_modules/@apollo/server/src/runHttpQuery.ts:232:27)
  at runPotentiallyBatchedHttpQuery (node_modules/@apollo/server/src/httpBatching.ts:85:12)
  at ApolloServer.executeHTTPGraphQLRequest (node_modules/@apollo/server/src/ApolloServer.ts:1058:14)

(^ this is because apollo server renames s/context/contextValue/ https://www.apollographql.com/docs/apollo-server/migration/#fields-on-graphqlrequestcontext)