Add staging-autofix STS policy for os repo (#80)

Signed-off-by: Nghia Tran <tcnghia@gmail.com>

Author: tcnghia

.github/chainguard/staging-autofix.sts.yaml

@@ -0,0 +1,14 @@
+issuer: https://accounts.google.com
+# autofix@staging-enforce-cd1e.iam.gserviceaccount.com
+subject: "118295070799166027529"
+
+permissions:
+  actions: read
+  checks: write
+  contents: write
+  pull_requests: read
+  statuses: read
+  workflows: write # Allow triggering actions when authoring commits.
+
+repositories:
+  - os