Generate attestation + refactor workflows (#1039)

.github/workflows/publish.yaml

@@ -1,3 +1,5 @@
+name: "Publish to Bazel Central Registry"
+
 on:
   # On manual trigger:
   workflow_dispatch:
@@ -6,6 +8,17 @@ on:
         required: true
         type: string
 
+  # Called from the release workflow:
+  workflow_call:
+    inputs:
+      tag_name:
+        required: true
+        type: string
+    secrets:
+      PUBLISH_TOKEN:
+        required: true
+        type: string
+
 jobs:    
   publish:
     uses: bazel-contrib/publish-to-bcr/.github/workflows/publish.yaml@v0.0.4