Allow marking rrweb as the top level even when in an iframe

[pauldambra]

if you have a page that you don't control which embeds your site in an iframe
and your site embeds another site in an iframe

so you have

• https:/one-domain
  • which embeds https://two-domain as an iframe
    • which itself embeds https://three-domain as an iframe

if https://two-domain was the top-level page we could support cross origin recording
but becaue it's an iframe we don't support it

this should need a change to rrweb but should be possible to support

see https://posthoghelp.zendesk.com/agent/tickets/12001

[pauldambra]

see also https://github.com/PostHog/rrweb/blob/posthog/packages/rrweb/src/record/index.ts#L95-L109