instance method to_query

Returns a string representation of the receiver suitable for use as a URL

query string:

    params = ActionController::Parameters.new({
      name: "David",
      nationality: "Danish"
    })
    params.to_query
    # => ActionController::UnfilteredParameters: unable to convert unpermitted parameters to hash

    safe_params = params.permit(:name, :nationality)
    safe_params.to_query
    # => "name=David&nationality=Danish"

An optional namespace can be passed to enclose key names:

    params = ActionController::Parameters.new({
      name: "David",
      nationality: "Danish"
    })
    safe_params = params.permit(:name, :nationality)
    safe_params.to_query("user")
    # => "user%5Bname%5D=David&user%5Bnationality%5D=Danish"

The string pairs `"key=value"` that conform the query string are sorted
lexicographically in ascending order.

: (*String?) -> String