add observability grant setter (#1214)

* add observability grant setter

* Create four-jokes-build.md

.changeset/four-jokes-build.md

@@ -0,0 +1,5 @@
+---
+"@livekit/protocol": patch
+---
+
+add observability grant setter

auth/accesstoken.go

@@ -93,6 +93,11 @@ func (t *AccessToken) SetInferenceGrant(grant *InferenceGrant) *AccessToken {
 	return t
 }
 
+func (t *AccessToken) SetObservabilityGrant(grant *ObservabilityGrant) *AccessToken {
+	t.grant.Observability = grant
+	return t
+}
+
 func (t *AccessToken) SetMetadata(md string) *AccessToken {
 	t.grant.Metadata = md
 	return t