Most API errors are present in the response body itself, which will be
sent to stdout normally, but if stdout is redirected somewhere (as it's
common with scripts), failed HTTP requests will likely sabotage the rest
of the script, but no useful info will be shown on stderr.
This makes it so all REST and GraphQL errors are always shown on stderr.
Additionally, this makes sure that the command exits with a nonzero
status on any GraphQL errors.
Reading from file via `-F foo=@myfile.txt` syntax would result in
`[]byte` Go type, which by default gets serialized to JSON in base64
format, which we don't want here.
Traverse all parameters and convert any `[]byte` into `string` before
JSON serialization.
