Add support for captions and subtitles

This example shows the difference between ggplot and ggplotly objects regarding the use of "labs".
Source: R for Data Science

library(ggplot2)
library(plotly)
p<-ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(color = class)) +
  geom_smooth(se = FALSE) +
  labs(
    title = "Fuel efficiency generally decreases with engine size",
    subtitle = "Two seaters (sports cars) are an exception because of their light weight",
    caption = "Data from fueleconomy.gov"
  );
p  # This is ok, a ggplot2 object
g <- ggplotly(p)
g  #  "labs()" Just showing title (centered) and  subtilte & caption are not even showing up

labs() OK

labs() not ok

Nenhum arquivo de implementação ou teste é indicado. Primeiro, reproduza o exemplo fornecido de ggplot2 e ggplotly e, em seguida, rastreie o caminho de conversão para labs(); considera-se concluído quando o gráfico resultante exibe tanto o subtítulo quanto a legenda como mostrado no ggplot de origem.