Refactor UPF entities to have consistent naming and string representations

Also, add slice ID into applications and interfaces entities

Change-Id: I159bcf04af1504b4e5c7210aa1402218fae3eb8f
(cherry picked from commit de1f1f7806716ac6e368e55eaf0b887ab89530d4)
diff --git a/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfEntityType.java b/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfEntityType.java
index e61abf1..2e9a26a 100644
--- a/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfEntityType.java
+++ b/core/api/src/main/java/org/onosproject/net/behaviour/upf/UpfEntityType.java
@@ -39,7 +39,7 @@
     }
 
     /**
-     * Returns a human readable representation of this UPF entity type (useful
+     * Returns a human-readable representation of this UPF entity type (useful
      * for logging).
      *
      * @return string