Expensive computed links force loaded in data explorer

[jackfischer]

We’ve been struggling with the data explorer in the UI quite a lot as pages often take 60 seconds+ to load. Looking at the underlying queries that are generated, this seems to be mostly due to traversing expensive computed links merely to populate the counts. As it stands, many of our important objects are left basically unusable.

Is it possible to load these separately, on an opt-in basis, or asynchronously?

For example, letting the user pare down what columns they'd like to see, even if only persisted in local storage, is a generally helpful feature in that it cleans up large views that also happens to solve this. Enabling or disabling computeds per se also solves it.

Consistency becomes an issue in the separate/async cases but maybe this could either be tolerated/messaged in the UI/opt in/be solved by opening a single deferrable transaction and performing both reads in separate queries?

Addressing this would also indirectly mitigate the impact of https://github.com/edgedb/edgedb-ui/issues/220

cc @ravintpillai