feat(a2a): Support A2A protocol calling by A2aAgent. (#172)

Author: KomachiSion

agentscope-dependencies-bom/pom.xml

@@ -232,6 +232,13 @@
                 <artifactId>redisson</artifactId>
                 <version>3.37.0</version>
             </dependency>
+            
+            <!-- A2A dependencies -->
+            <dependency>
+                <groupId>io.github.a2asdk</groupId>
+                <artifactId>a2a-java-sdk-client</artifactId>
+                <version>0.3.2.Final</version>
+            </dependency>
 
             <!-- Jedis client for Redis-based session implementation -->
             <dependency>

agentscope-extensions/agentscope-extensions-a2a/agentscope-extensions-a2a-agent/pom.xml

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2024-2025 the original author or authors.
+  ~
+  ~ Licensed 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.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>io.agentscope</groupId>
+        <artifactId>agentscope-extensions</artifactId>
+        <version>${revision}</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+    
+    <name>AgentScope Java - Extensions - A2A Agent</name>
+    <description>AgentScope Extensions - Agent to call remote Agent by A2A protocol</description>
+    <artifactId>agentscope-extensions-a2a-agent</artifactId>
+    
+    <dependencies>
+        <dependency>
+            <groupId>io.agentscope</groupId>
+            <artifactId>agentscope-core</artifactId>
+            <version>${revision}</version>
+        </dependency>
+        
+        <dependency>
+            <groupId>io.github.a2asdk</groupId>
+            <artifactId>a2a-java-sdk-client</artifactId>
+        </dependency>
+    </dependencies>
+
+</project>