Specifying the implications of profiling a graph submission.

[EwanC]

Motivated by feedback at - intel#5626 (comment)

We should specify what it means to get profiling information from the event returned from the queue submission of a graph. All the wording in the core SYCL spec around profiling is centred on command-groups - https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#table.event.profilinginfo - so we can't defer to that.