Update insertable streams section to WebRTC Encoded transforms

• I understand that issues created here are only relevant to the samples in this repo - not browser or SDK bugs
• I have provided steps to reproduce
• I have provided browser name and version
• I have provided a link to the sample here or a modified version thereof

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Browser affected

Browser name including version: Firefox 119.0a1. Also Chrome, Safari.

Description

Insertable streams samples represent a deprecated API, replaced by https://w3c.github.io/webrtc-encoded-transform/. Those are implemented from FF117

The desired result is that is it is easy to try out these examples and that they reflect the current standards.