[Feature request] Add option to define code button alignment

[fschaffner]

Many thanks for creating and maintaining this package!

Would it be possible to add an option that defines where on the page the "Show code" button will be located if using the option "code-fold: true" when rendering HTML? I find that having the code button on the left breaks my reading flow, and I would prefer if the button was located in the center or on the right of the page.

I would propose to add an option "code-align" with can take the values "left", "center", or "right" (as illustrated below).

Apologies if this feature already exists, I couldn't find it in the documentation.

---
title: "Title"
format:
  html:
    code-fold: true
    code-summary: "Show code"
    code-align: "right" # Proposed options: "left", "center", "right"
---

```{r}
library("ggplot2")
dat <- data.frame(cond = rep(c("A", "B"), each=10),
                  xvar = 1:20 + rnorm(20,sd=3),
                  yvar = 1:20 + rnorm(20,sd=3))

ggplot(dat, aes(x=xvar, y=yvar)) +
    geom_point(shape=1) + 
    geom_smooth() 
```

[jjallaire]

There isn't currently an option to relocate the code fold control, but we'll definitely consider adding one (I took a quick look at the html <details> tag we use under the hood is not trivially relocatable -- some CSS hacks would be required and we want to make sure they aren't breaking other things.

[fschaffner]

Okay, thanks for having a look and for considering this!