Offer a way to configure which chromium to use for feature that rely on it (diagram snapshot)

[cderv]

This is a macro issue that should solve all the report

• Quarto deos not find chromium if installed through flatpak #2980
• Quarto does not find chromium on Arch Linux, even though it is installed #4648
• Detect Microsoft Edge install (if Google Chrome isn't) on MacOS #10162

For reference, current state in some R package that also need to use chromium (as discussed in #4648 (comment))

• pagedown::find_chrome() will look for chrome for each OS, on Linux checking for c('google-chrome', 'chromium-browser', 'chromium', 'google-chrome-stable') and using first found. Setting env var PAGEDOWN_CHROME allow to specific a specific one to use
• chromote::find_chrome() will so similarly, looking for google-chrome, chromium-browser and chromium , or using CHROMOTE_CHROME if set.

Having a QUARTO_CHROMIUM environment variable to look for, and use this path if set seems a good solution.

[ralmond]

This looks like a good solution. It would be useful to add a help file or a link to a web page which shows possible places to look for chromium installation, as I suspect that not all users experiencing this problem will know all of the places to look.