Feature request: Add Auto Height

[Baltazar5000]

Hello.

Add Auto Height, please.

For example, in Converter.js:

        if (options.hasOwnProperty('height')) {
            if(options.height == 'auto'){
                let bodyHeight = await page.evaluate(() => document.body.scrollHeight);
                options.height = bodyHeight;
            }
        }

        return this._getPdf(page, options)