[lightbox] Allow to configure lightbox image size

Bug description

When using lightbox: true and fig-format: svg, the lightbox image of an R-plot will have the same size as the original one (i.e., there is no zoom-in). When removing fig-format: svg in the code below, everyting works as intended.

Steps to reproduce

---
title: "Untitled"
editor: visual
format: 
  html:
    lightbox: true
    fig-format: svg
---

```{r}
plot(1:10)
```

Expected behavior

There should be a zoom-in effect.

Actual behavior

No zoom-in effect.

Your environment

• RStudio 2024.04.2+764
• Quarto 1.5.54 (C:/Users/meierluk/AppData/Local/Programs/Quarto/bin/quarto.exe)

Quarto check output

Quarto 1.5.54
[>] Checking versions of quarto binary dependencies...
      Pandoc version 3.2.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.41.0: OK
      Typst version 0.11.0: OK
[>] Checking versions of quarto dependencies......OK
[>] Checking Quarto installation......OK
      Version: 1.5.54
      Path: C:\Users\meierluk\AppData\Local\Programs\Quarto\bin
      CodePage: 1252

[>] Checking tools....................OK
      TinyTeX: v2024.04
      Chromium: (not installed)

[>] Checking LaTeX....................OK
      Using: TinyTex
      Path: C:\Users\meierluk\AppData\Roaming\TinyTeX\bin\windows\
      Version: 2024

[>] Checking basic markdown render....OK

[>] Checking Python 3 installation....OK
      Version: 3.10.0
      Path: C:/Users/meierluk/AppData/Local/Programs/Python/Python310/python.exe
      Jupyter: 5.7.2
      Kernels: julia-1.9, python3

(|) Checking Jupyter engine render....Traceback (most recent call last):
  File "C:\Users\meierluk\AppData\Local\Programs\Quarto\share\jupyter\jupyter.py", line 21, in <module>
    from notebook import notebook_execute, RestartKernel
  File "C:\Users\meierluk\AppData\Local\Programs\Quarto\share\jupyter\notebook.py", line 15, in <module>
    from yaml import safe_load as parse_string
ModuleNotFoundError: No module named 'yaml'
[>] Checking Jupyter engine render....OK

Start by rendering the supplied minimal Quarto document twice, once with fig-format: svg and once without it, then compare the generated HTML lightbox behavior. Trace the lightbox handling for R plots and SVG figures; done means the SVG case provides the same zoom-in effect as the non-SVG case.