Use the official unit string for the 'b' when creating the ByteCount …

…string. (#3993)

Signed-off-by: David Venable <dlv@amazon.com>

data-prepper-api/src/main/java/org/opensearch/dataprepper/model/types/ByteCount.java

@@ -163,6 +163,6 @@ public boolean equals(final Object otherObject) {
      */
     @Override
     public String toString() {
-        return bytes + "b";
+        return bytes + Unit.BYTE.unitString;
     }
 }