[1.x] Update webrtc-adapter to version 9

[gjanblaszczyk]

What version of Janus is this happening on?
Latest

Have you tested a more recent version of Janus too?
Yes

Was this working before?
No

Is there a gdb or libasan trace of the issue?

Additional context
The project uses an older version 8, but the new version 9 is available https://www.npmjs.com/package/webrtc-adapter/v/9.0.1, https://github.com/webrtcHacks/adapter/releases.
It would be nice to see the latest version of webrtc-adapter in the janus-gateway project.

[lminiero]

I understand it would be nice to have, but to be honest it's not a priority for me. If you care about that, please do feel free to test the new version of the adapter with our demos, to see if it causes any regressions, and submit a PR we can evaluate. An example of a PR that last changed the adapter is #3256.