fix: clarify PGRST204 error message

[steve-chavez]

Closes #3361

[wolfgangwalther]

This might be technically correct, but is not always an improvement. When your schema cache is up2date, but the column does really not exist... you might be led the wrong way here, assuming you have to reload the schema cache etc.

I'm not saying this change is bad - but it's also not always an improvement. Not sure what to do.

[steve-chavez]

We already have the "schema cache" message in others errors. Which could be misleading in the same way.

postgrest/test/spec/Feature/Query/QuerySpec.hs

Line 617 in 594b41a

"message":"Could not find a relationship between 'car_model_sales_202101' and 'car_models' in the schema cache"} |]

postgrest/test/spec/Feature/Query/RpcSpec.hs

Line 213 in 594b41a

"message":"Could not find the function test.sayhell without parameters in the schema cache",

but it's also not always an improvement. Not sure what to do.

Yeah, but at least being consistent is a bit better.