ci: setup Aspect Workflows

Includes a Buildbarn cache cluster so we are dogfooding.

buildbarn/bb-storage#252 followup

Author: alexeagle

.aspect/workflows/config.yaml

@@ -0,0 +1,6 @@
+# See https://docs.aspect.build/workflows/configuration
+tasks:
+  - buildifier
+  - test
+notifications:
+  github: {}