Write subscription results under ROOT_SUBSCRIPTION ID instead of ROOT_QUERY

[stubailo]

This will help show in the Apollo dev tools whether data came from a subscription or query.

[dko-slapdash]

Could you please clarify, is it true (and on intent) that ROOT_SUBSCRIPTION is never read anywhere in the code, it's only written?

The following search shows that there are no more references to ROOT_SUBSCRIPTION (including dev tools): https://github.com/search?q=org%3Aapollographql+ROOT_SUBSCRIPTION&unscoped_q=ROOT_SUBSCRIPTION

[jedwards1211]

Not only that, subscription data shouldn't overwrite cached query data automatically anyway, right?