Add webp to screenshot options

[jonchurch]

closes: #5348

Not sure since when, but webp is an option in Page.captureScreenshot now.

All that is needed is to allow users to pass type: "webp" through.

After making said change to allow passing webp through as an option, this code successfully creates webp screenshots using either type: "webp" or using the .webp extension from the filepath.

const puppeteer = require('puppeteer')

async function run() {
const browser = await puppeteer.launch()
  const page = await browser.newPage()
  await page.setViewport({ width: 1280, height: 800 })
  await page.goto('https://www.nytimes.com/')
  await page.screenshot({ path: `${__dirname}/nytimes.webp`, fullPage: true, type: 'webp'})
  await page.screenshot({ path: `${__dirname}/nytimes_alt.webp`, fullPage: true,})
  await browser.close()
}

run().then(() => console.log('done')).catch(console.log)

Happy to take any help getting this mergeable, ie writing tests.

I'd upload a webp here but github doesn't support them!

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[jonchurch]

@googlebot I signed it!

[jschfflr]

Thanks for your contribution! The change looks good from a technical point of view but it would be great if you could also update the documentation (docs/api.md) and add a unit test (see screenshot.spec.ts). Thanks!

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[jschfflr]

@googlebot I consent.

[jschfflr]

@jonchurch I already went ahead and addressed the outstanding comments to get this into the next release :)

[jonchurch]

@jschfflr Yay! Thank you for getting this over the finish line 🥇

[jschfflr]

Sure, happy to help!