[#9529] feat(server): Add server-side REST interface for UDFs

This PR implements the server-side REST API for User-Defined Functions (UDFs).

Changes include:
- Add FunctionDTO and related DTO classes for function metadata
- Add FunctionRegisterRequest and FunctionUpdateRequest for API requests
- Add FunctionResponse for API responses
- Add FunctionOperations REST endpoint with register, get, update, delete operations
- Add exception handlers for function-related errors
- Add comprehensive unit tests for all new components

Author: mchades

common/src/main/java/org/apache/gravitino/dto/function/FunctionColumnDTO.java

@@ -0,0 +1,146 @@
+/*
+ * 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.gravitino.dto.function;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.annotation.JsonSerialize;
+import javax.annotation.Nullable;
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+import org.apache.gravitino.function.FunctionColumn;
+import org.apache.gravitino.json.JsonUtils;
+import org.apache.gravitino.rel.types.Type;
+
+/** DTO for function column. */
+@Getter
+@EqualsAndHashCode
+public class FunctionColumnDTO {
+
+  @JsonProperty("name")
+  private String name;
+
+  @JsonProperty("dataType")
+  @JsonSerialize(using = JsonUtils.TypeSerializer.class)
+  @JsonDeserialize(using = JsonUtils.TypeDeserializer.class)
+  private Type dataType;
+
+  @Nullable
+  @JsonProperty("comment")
+  private String comment;
+
+  private FunctionColumnDTO() {}
+
+  private FunctionColumnDTO(String name, Type dataType, String comment) {
+    this.name = name;
+    this.dataType = dataType;
+    this.comment = comment;
+  }
+
+  /**
+   * Convert this DTO to a {@link FunctionColumn} instance.
+   *
+   * @return The function column.
+   */
+  public FunctionColumn toFunctionColumn() {
+    return FunctionColumn.of(name, dataType, comment);
+  }
+
+  /**
+   * Create a {@link FunctionColumnDTO} from a {@link FunctionColumn} instance.
+   *
+   * @param column The function column.
+   * @return The function column DTO.
+   */
+  public static FunctionColumnDTO fromFunctionColumn(FunctionColumn column) {
+    return new FunctionColumnDTO(column.name(), column.dataType(), column.comment());
+  }
+
+  @Override
+  public String toString() {
+    return "FunctionColumnDTO{"
+        + "name='"
+        + name
+        + '\''
+        + ", dataType="
+        + dataType
+        + ", comment='"
+        + comment
+        + '\''
+        + '}';
+  }
+
+  /** Builder for {@link FunctionColumnDTO}. */
+  public static class Builder {
+    private String name;
+    private Type dataType;
+    private String comment;
+
+    /**
+     * Set the column name.
+     *
+     * @param name The column name.
+     * @return This builder.
+     */
+    public Builder withName(String name) {
+      this.name = name;
+      return this;
+    }
+
+    /**
+     * Set the column data type.
+     *
+     * @param dataType The column data type.
+     * @return This builder.
+     */
+    public Builder withDataType(Type dataType) {
+      this.dataType = dataType;
+      return this;
+    }
+
+    /**
+     * Set the column comment.
+     *
+     * @param comment The column comment.
+     * @return This builder.
+     */
+    public Builder withComment(String comment) {
+      this.comment = comment;
+      return this;
+    }
+
+    /**
+     * Build the {@link FunctionColumnDTO}.
+     *
+     * @return The function column DTO.
+     */
+    public FunctionColumnDTO build() {
+      return new FunctionColumnDTO(name, dataType, comment);
+    }
+  }
+
+  /**
+   * Create a new builder.
+   *
+   * @return A new builder.
+   */
+  public static Builder builder() {
+    return new Builder();
+  }
+}