@ modifier returns empty results when used inside PromQL function

[Harkishen-Singh]

Describe the bug
In PromQL, go_goroutines @ end() works, but delta(go_goroutines[5m] @ end()) does not work (It works in Prometheus).

To Reproduce

Run Promscale with Prometheus pushing recent data and run the above queries. You will notice that the second query works in Prometheus data source but not in Promscale data source.

Expected behavior
delta(go_goroutines[5m] @ end()) or @ modifier in general inside any PromQL function should work in Promscale.

Screenshots

[stormybriggs1]

Would love to see this short-coming fixed. We have some graphs that are empty after being ported to Promscale due to this bug.