document non-determinisme in gql calls

Created by: unclejustin

Context

We had an issue where results from the backend were expected to be deterministic but they are not. The UI had this assumption but did not enforce it. It prompted a discussion of "how could we have known". The idea here is to at least get a rough idea of other "assumptions" on the frontend.

This PR simply comments where some assumptions are made. At some point, we should probably offload some of the sortings that are done on the FE to the backend and write tests to assert that is true.

Closes https://github.com/sourcegraph/sourcegraph/issues/34912

Test plan

N/A This just adds comments