Consider a function to use in the knit YAML fields to modify version used when knitting in RStudio IDE

[cderv]

Following ideas discussed in rstudio/rmarkdown#2513 (comment)

Aim is to simplify this

---
title: test
output: 
  html_document:
    self_contained: true
knit: ( \(input, ...) pandoc::with_pandoc_version("2.7.3", rmarkdown::render(input)) )
---

# Test