[infra] Allow project-libyuv-admins group to trigger LED tasks

"role/swarming.taskTriggerer" gives "swarming.tasks.createInRealm" permission.
https://source.chromium.org/chromium/infra/infra/+/main:luci/appengine/auth_service/realms/permissions.py;l=114;drc=36516367cd70f195935ffd933d939e770e3b2c65

This fixes the auth error in "led launch".
http://screen/58TYKnHALbRUQKb

Bug: b:255217089
Change-Id: Idbfc06e7ad8a94caac9bfd1fe473c60d6e4addf6
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/3990134
Reviewed-by: Christoffer Jansson <jansson@chromium.org>
Commit-Queue: Junji Watanabe <jwata@google.com>

infra/config/main.star

@@ -79,6 +79,10 @@ luci.project(
         acl.entry(acl.BUILDBUCKET_OWNER, groups = ["project-libyuv-admins"]),
     ],
     bindings = [
+        luci.binding(
+            roles = "role/swarming.taskTriggerer", # for LED tasks.
+            groups = "project-libyuv-admins",
+        ),
         luci.binding(
             roles = "role/configs.validator",
             users = "libyuv-try-builder@chops-service-accounts.iam.gserviceaccount.com",

infra/config/realms.cfg

@@ -38,6 +38,10 @@ realms {
     role: "role/scheduler.reader"
     principals: "group:all"
   }
+  bindings {
+    role: "role/swarming.taskTriggerer"
+    principals: "group:project-libyuv-admins"
+  }
 }
 realms {
   name: "ci"