build: switch to playwright image (and python3.10)

[uptickmetachu]

Changes:

• Adds playwright to the build (Increases image size to 2GB :()
• Adds browser_url option for browser based rendering of a remote url
• Adds renderer option (takes prince or playwright). When rendering browser_url playwright is used to fetch html and then feed into prince
• Adds browser_headers option. A mapping of str->str for additional browser headers when viewing a page. Useful for browser based authentication.
• Adds ./splat_cli.py which can be used to invoke the dockerised splat lambda (or url) and generate pdfs. Useful for comparing princexml and playwright renderers.

[bayangan1991]

Can't see any issues here.

Would be good to see a demo of it working if you have a chance