Revert "Remove oscavmgr-launch script"

This reverts commit 14e2a8afa12374ca7111fe134c59d981f9ccd2f6.

scripts/oscavmgr-launch.sh

···
+#!/usr/bin/env bash
+
+# stop VrcAdvert after OscAvMgr quits
+trap 'jobs -p | xargs kill' EXIT
+
+VrcAdvert OscAvMgr 9402 9002 --tracking &
+
+# If using WiVRn
+oscavmgr openxr
+
+## If using ALVR
+#oscavmgr alvr
+
+## If using Project Babble and/or EyeTrackVR
+#oscavmgr babble