Allow clients to specify video layers mode. (#1158)

* Allow clients to specify video layers mode.

The main issue is distinguishing between one RTP streaming carry
multiple spatial layers (example SVC codecs) vs one spatial layer
(codecs that are typically simulcast). The enum names are long, but
wanted them to be clear.

* generated protobuf

* Create unlucky-birds-drive.md

* comment

* generated protobuf

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Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

Author: boks1971

.changeset/unlucky-birds-drive.md

@@ -0,0 +1,6 @@
+---
+"@livekit/protocol": patch
+"github.com/livekit/protocol": patch
+---
+
+Allow clients to specify video layers mode.