feat(curations): Set a version of 'listenablefuture' as metadata only

Signed-off-by: Frank Viernau <[email protected]>

Author: fviernau

curations/Maven/com.google.guava/listenablefuture.yml

@@ -0,0 +1,5 @@
+- id: "Maven:com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava"
+  curations:
+    comment: |
+      This library is empty as it is version string suggests.
+    is_metadata_only: true