[core] Add basic implementation to support REST Catalog

paimon-core/src/main/java/org/apache/paimon/rest/requests/ConfigRequest.java

@@ -20,7 +20,12 @@
 
 import org.apache.paimon.rest.RESTRequest;
 
+import org.apache.paimon.shade.com.fasterxml.jackson.annotation.JsonCreator;
+import org.apache.paimon.shade.jackson2.com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+
 /** Request to get config. */
+@JsonIgnoreProperties(ignoreUnknown = true)
 public class ConfigRequest implements RESTRequest {
+    @JsonCreator
     public ConfigRequest() {}
 }

paimon-core/src/main/java/org/apache/paimon/rest/responses/ConfigResponse.java

@@ -20,12 +20,21 @@
 
 import org.apache.paimon.rest.RESTResponse;
 
+import org.apache.paimon.shade.com.fasterxml.jackson.annotation.JsonProperty;
+import org.apache.paimon.shade.jackson2.com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+
+import java.beans.ConstructorProperties;
 import java.util.Map;
 
 /** Response for getting config. */
+@JsonIgnoreProperties(ignoreUnknown = true)
 public class ConfigResponse implements RESTResponse {
+    private static final String FIELD_DEFAULTS = "defaults";
+
+    @JsonProperty(FIELD_DEFAULTS)
     private Map<String, String> defaults;
 
+    @ConstructorProperties({FIELD_DEFAULTS})
     public ConfigResponse(Map<String, String> defaults) {
         this.defaults = defaults;
     }

paimon-core/src/test/java/org/apache/paimon/rest/HttpClientTest.java

@@ -0,0 +1,22 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.paimon.rest;
+
+/** Test for {@link HttpClient}. */
+public class HttpClientTest {}