Add "Supported By Posit" badge to pak website

## Overview This PR adds the "Supported by Posit" badge to the pak website. ## Background We've recently started adding a "Supported by Posit" badge across all Posit package websites to create a more cohesive brand presence. The badge appears on the far right of the top navigation bar or at the bottom of the hamburger menu. It links to Posit’s main website. @hadley is involved with this initiative. The following websites already have the "Supported by Posit" badge: [ggplot2](https://ggplot2.tidyverse.org), [Great Tables](https://posit-dev.github.io/great-tables/articles/intro.html), [gt](https://gt.rstudio.com), [Plotnine](https://plotnine.org), [Pointblank](https://posit-dev.github.io/pointblank/), [pointblank](https://rstudio.github.io/pointblank/), and [Quarto](https://quarto.org). See https://posit-dev.github.io/supported-by-posit/ for more information. ## Changes - Added a line to `_pkgdown.yml` to include the JavaScript file - Standardized indentation in `_pkgdown.yml` ## Screenshots At 1200px browser width:  At 992px browser width:  At 991px browser width: