Bug 1665379 - Add CI workerType for apple silicon build on x86 apple hardware macosx64-aarch64/opt. r=jmaher,glandium,aki,bhearsum DONTBUILD

Differential Revision: https://phabricator.services.mozilla.com/D96261

taskcluster/ci/config.yml

@@ -563,6 +563,14 @@ workers:
             implementation: docker-worker
             os: linux
             worker-type: 't-linux-xlarge'
+        b-osx-1015:
+            provisioner: releng-hardware
+            implementation: generic-worker
+            os: macosx
+            worker-type:
+                by-level:
+                    '3': 'gecko-3-b-osx-1015'
+                    default: 'gecko-1-b-osx-1015'
         t-osx-1014-pgo:
             provisioner: releng-hardware
             implementation: generic-worker