[Bug] CloudEvents variable names do not support underscores

[mxsm]

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• I had searched in the issues and found no similar issues.

Environment

Windows

EventMesh version

master

What happened

CloudEvents variable names do not support underscores。

How to reproduce

    public static void main(String[] args) {
        CloudEvent.Builder builder = CloudEvent.newBuilder().setId(RandomStringUtils.generateUUID()).setSpecVersion("1.0")
            .putAttributes(ProtocolKey.GRPC_RESPONSE_CODE, CloudEventAttributeValue.newBuilder().setCeString("").build())
            .putAttributes(ProtocolKey.GRPC_RESPONSE_MESSAGE,
                CloudEventAttributeValue.newBuilder().setCeString("").build())
            .putAttributes(ProtocolKey.GRPC_RESPONSE_TIME, CloudEventAttributeValue.newBuilder()
                .setCeTimestamp(Timestamp.newBuilder().setSeconds(1).build()).build());
        final io.cloudevents.CloudEvent cloudEvent = switchEventMeshCloudEvent2CloudEvent(builder.build());
    }

Debug logs

Exception in thread "main" io.cloudevents.rw.CloudEventRWException: Invalid extensions name: status_code
at io.cloudevents.rw.CloudEventRWException.newInvalidExtensionName(CloudEventRWException.java:122)
at io.cloudevents.core.impl.BaseCloudEventBuilder.withExtension(BaseCloudEventBuilder.java:121)
at io.cloudevents.core.v1.CloudEventBuilder.withContextAttribute(CloudEventBuilder.java:176)
at io.cloudevents.protobuf.ProtoDeserializer.read(ProtoDeserializer.java:73)
at io.cloudevents.rw.CloudEventReader.read(CloudEventReader.java:43)
at io.cloudevents.protobuf.ProtobufFormat.deserialize(ProtobufFormat.java:64)
at io.cloudevents.core.format.EventFormat.deserialize(EventFormat.java:56)
at org.apache.eventmesh.client.grpc.util.EventMeshCloudEventBuilder.switchEventMeshCloudEvent2CloudEvent(EventMeshCloudEventBuilder.java:272)
at org.apache.eventmesh.client.grpc.util.EventMeshCloudEventBuilder.main(EventMeshCloudEventBuilder.java:294)

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• Yes I am willing to submit a PR!

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