ci: Add ANGULAR_PACKAGE to snapshot builds

Ivy snapshots no longer contain metadata.json which breaks the detection logic for
Angular Package Format (APF) in npm/yarn install.
This PR adds ANGULAR_PACAKGE as a magic file to denote APF.
See bazel-contrib/rules_nodejs#927

scripts/ci/publish-build-artifacts.sh

@@ -70,6 +70,7 @@ function publishRepo {
   fi
   echo `date` > $REPO_DIR/BUILD_INFO
   echo $SHA >> $REPO_DIR/BUILD_INFO
+  echo 'This file is used by the npm/yarn_install rule to detect APF' > $REPO_DIR/ANGULAR_PACKAGE
 
   (
     cd $REPO_DIR && \