Requirement request-data-count

[filippofinke]

Currently, the count functionality is implemented only by the parser side and so it is not working properly.

http://[localhost:8018/v1.1/Datastreams?$count=true](http://localhost:8018/v1.1/Datastreams?$count=true)

Error generated by PostgREST

{
  "code": 404,
  "type": "error",
  "message": "\"failed to parse filter (true)\" (line 1, column 1)"
}

https://docs.ogc.org/is/18-088/18-088.html#requirement-request-data-count