test(load): update error loadtest endpoint to generate hint

[taimoorzaeem]

This endpoint didn't generate error hint which is not desired for loadtest. Now it does. As discussed in #4837 (comment).

postgrest-with-pg-18 -f test/load/fixtures.sql postgrest-run

curl -i localhost:3000/rpc/call_me_x?name=John

HTTP/1.1 404 Not Found
Date: Thu, 23 Apr 2026 18:22:20 GMT
Server: postgrest/15 (pre-release)
Content-Type: application/json; charset=utf-8
Content-Length: 282
Proxy-Status: PostgREST; error=PGRST202

{
  "code":"PGRST202",
  "details":"Searched for the function test.call_me_x with parameter name, but no matches were found in the schema cache.",
  "hint":"Perhaps you meant to call the function test.call_me",
  "message":"Could not find the function test.call_me_x(name) in the schema cache"
}

[taimoorzaeem]

I think another issue in our loadtest (errors) is that we barely have any tables and functions in our loadtest fixtures (2 tables and 1 function), which is why the loadtest result looks unbudged. We should have more tables and functions to accurately load test the hint generation.

EDIT: We should open another issue for this, I guess this PR can be merged, since it now generates the hint.