获取群组成员列表

{
    "code": 1,
    "message": "获取群成员成功",
    "data": [
        {
            "user_id": "user_123",
            "member_type": "owner",
            "member_nickname": "群主",
            "join_time": "2024-01-01T12:00:00Z"
        },
        {
            "user_id": "user_456",
            "member_type": "admin",
            "member_nickname": "管理员",
            "join_time": "2024-01-02T12:00:00Z"
        },
        {
            "user_id": "user_789",
            "member_type": "member",
            "member_nickname": "普通成员",
            "join_time": "2024-01-03T12:00:00Z"
        }
    ]
}