100ms loading time is not enough for certain documents

[IansGithubAcc]

The line below lets playright wait for 100ms to load the page before it does a print screen.

nbconvert/nbconvert/exporters/webpdf.py

Line 124 in 216550b

await page.wait_for_timeout(100)

For small documents this might be enough, but I've encountered various notebooks that were not properly represented due to the page not being fully loaded.

I suggest to add an argument/config such that this value can be adjusted by the user.