SL-15612 Check for SKIP_NOTARIZATION evn. variable

indra/newview/installers/darwin/apple-notarize.sh

 #!/bin/sh
+if [ -n $SKIP_NOTARIZATION ]; then
+    echo "Skipping notarization"
+    exit 0
+fi
+
 CONFIG_FILE="$build_secrets_checkout/code-signing-osx/notarize_creds.sh"
 if [ -f "$CONFIG_FILE" ]; then
     source $CONFIG_FILE