Document updateQuery and updateFragment

Document the new `updateQuery` and `updateFragment` cache API changes added in https://github.com/apollographql/apollo-client/pull/8382.

Doc sections that should be updated:

- [Reading and writing data to the cache](https://www.apollographql.com/docs/react/api/cache/InMemoryCache)
- [InMemoryCache API](https://www.apollographql.com/docs/react/caching/cache-interaction/)