Indicate that the scalability mode is supported if the scalability config exists. Bug: webrtc:13960 Change-Id: I6f42da6c9bbff1322ec5c3e3a68c7e031606da86 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/262981 Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Commit-Queue: Åsa Persson <asapersson@webrtc.org> Cr-Commit-Position: refs/heads/main@{#36989}