fix(graph): HttpNode supports user-defined variable filtering methods.

[yaohuitc]

Describe what this PR does / why we need it

在通过HttpNode实现WebHook发送通知信息场景，请求的文本内容是需要包含/n等字符的；因此，做以下两点建议：
1、将json处理的objectMapper允许用户自定义，例如自定义如下objectMapper：
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(JsonReadFeature.ALLOW_UNESCAPED_CONTROL_CHARS.mappedFeature());
2、对变量的过滤替换规则也允许由用户自定义；当然如果是state中的全局变量，更建议是在KeyStrategy中进行处理。本次提交为兼容原先逻辑，保留原默认的替换方式

参考数据按理：
String message = """今日AI工单智能助手总结

						当天合计工单: %d条，有效解决率: %s, 客户平均满意度（0～5）评估：%d
						""";

Does this pull request fix one issue?

Describe how you did it

Describe how to verify it

build a HttpNode with objectMapper and variableFilter, run it
HttpNode.builder()
.method(HttpMethod.POST)
.url(url)
.body(formBody)
.outputKey("message_sender_result")
.objectMapper(objectMapper)
.variableFilter(variable -> variable)
.build();

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