Allow passing options directly to Puppeteer's Page.pdf() function

[jerboa88]

Allow options to be passed directly to Puppeteer's Page.pdf() like so:

setDefaultOptions({
  puppeteer: {
    pdf: {
      printBackground: false,
      scale: 1.5, 
      tagged: false,
      // ...
    },
    // ...
  },
  // ...
})

Allowing arbitrary options to be passed will give user's more flexibility in case they need to customize the behavior of Page.pdf() for their use case.

Options important for correct behavior of the plugin like path, width, and height should overwrite user-provided options. printBackground should have a default value of true to ensure similar behavior as Page.screenshot(), but we should allow user's to override this value.