[Feature] Proper support for @live directive + support @defer directive

[alexstrat]

As of today, any query and the whole query is considered as @live query (ie queries for which we emit results when it changes).

I think proper support for the @live directive should look like this:

• result of executing a query is not live if the directive is not present: it produces an Observable that completes after the first result
• only specific fields can be marked as @live or the whole operation can be marked as @live

Support for @defer directive.

[DanielMSchmidt]

Sounds like a good idea, we just need to add a pipe(take(1)) if there is a directive present