scylla-apiclient: Add Date json serializer helper

To handle RFC8601 formattedd dates in JAXB

src/main/java/com/scylladb/jmx/utils/DateXmlAdapter.java

@@ -0,0 +1,19 @@
+package com.scylladb.jmx.utils;
+
+import java.time.Instant;
+import java.util.Date;
+
+import javax.xml.bind.annotation.adapters.XmlAdapter;
+
+public class DateXmlAdapter extends XmlAdapter<String, Date> {
+    @Override
+    public String marshal(Date v) throws Exception {
+        return Instant.ofEpochMilli(v.getTime()).toString();
+    }
+
+    @Override
+    public Date unmarshal(String v) throws Exception {
+        return new Date(Instant.parse(v).toEpochMilli());
+    }
+
+}