Switch Optional.ofNullable() to Optional.fromNullable() in EppMetric

The latter is the canonical way to call it; the former is not available in
public Guava (and is just a pass-through to fromNullable anyway).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132441956

java/google/registry/monitoring/whitebox/EppMetric.java

@@ -69,11 +69,11 @@ public abstract class EppMetric implements BigQueryMetric {
         requestId,
         startTimestamp,
         endTimestamp,
-        Optional.ofNullable(commandName),
-        Optional.ofNullable(clientId),
-        Optional.ofNullable(privilegeLevel),
-        Optional.ofNullable(eppTarget),
-        Optional.ofNullable(status),
+        Optional.fromNullable(commandName),
+        Optional.fromNullable(clientId),
+        Optional.fromNullable(privilegeLevel),
+        Optional.fromNullable(eppTarget),
+        Optional.fromNullable(status),
         attempts);
   }