Add custom knitr hook to simplify ggtibble plotting in reports

[billdenney]

Make a chunk like the following work:

```{r ggtibble=ggtibble_object}
```

where it will expand to do the following:

```{r, fig.cap = ggtibble_object$caption}
knit_print(ggtibble_object)
```

[billdenney]

See https://stackoverflow.com/questions/71960750/is-it-possible-to-change-the-fig-cap-chunk-option-within-knitr/78387157#78387157