[Replay] Expose rrweb `recordCrossOriginIframes` under `_experiment`

[bruno-garcia]

Description

See: #11858

Came up a few times and it's a feature supported by rrweb.
This can have some challenges that will put more pressure in supporting this feature, since we had issues early on when testing it.

But adding this under _experiment so folks can try it out and unblock themselves while communicating this isn't a GA functionality is a good next step

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #14916, which was included in the 9.2.0 release.