feat: accepts headers for puppeteer goto request

[jaysonmulwa]

Accepts an object with a list of headers if present.

For example:

`
const headersObj = {
"accept": "application/json",
"accept-encoding": "gzip, deflate, br",
"accept-language": "en-US,en;q=0.9,en;q=0.8"
};

let file = { url: "http://localhost:3000", headers: headersObj };
html_to_pdf.generatePdf(file, options).then(pdfBuffer => {
console.log("PDF Buffer:-", pdfBuffer);
});
`