agent_simulation: add audio mode (#1627)

* agent_simulation: carry mode on Create request and run info

Unspecified stays TEXT, so existing callers are unaffected.

* generated protobuf

* Rename channel -> mode

Co-authored-by: David Zhao <david@davidzhao.com>
Co-authored-by: Arseny Boykov <36469655+Bobronium@users.noreply.github.com>

* generated protobuf

---------

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

Author: 3 people

.changeset/audio-simulation-mode.md

@@ -0,0 +1,7 @@
+---
+"github.com/livekit/protocol": minor
+---
+
+agent simulation: add SimulationMode to the Create request and run info, so a
+run can request audio mode. Unspecified stays TEXT, so existing callers are
+unaffected.