Function build_graphql_document 

pub fn build_graphql_document(
    cmd: &CommandDef,
    values: &BTreeMap<String, Value>,
    stdin_vars: Option<Map<String, Value>>,
    schema: &Value,
    fields_override: Option<&str>,
) -> Result<(String, Map<String, Value>, String)>

Build document + variables from parsed CLI args.