Different error codes in case of singular failure

[steve-chavez]

Problem

When Singular fails, we return a 406 status code and:

{
  "code": "PGRST116",
  "message": "Cannot coerce the result to a single JSON object",
  "details": "The result contains 0 rows",
  "hint": null
}

But the error code doesn't differentiate between 0 or multiple rows, the only way to do is to parse the error message, which is fickle.

Solution

Return different error codes for each case, let's use the next available codes from group 1. PGRST129 for the 0 case and PGRST130 for multiple.

This would be a breaking change because PGRST116 would no longer be used.