AMQContentHeader toString uses dashes instead of underscores for property names

The com.rabbitmq.client.impl.AMQContentHeader has the following toString implementation

    @Override public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("#contentHeader<").append(getClassName()).append(">");
        this.appendPropertyDebugStringTo(sb);
        return sb.toString();
    }

It generates strings like this

#contentHeader<basic>(content-type=application/json, content-encoding=UTF-8, headers={topic=DOWNLOAD_AND_INSTALL, content-type=application/json, type=EVENT, tenant=DEFAULT, __TypeId__=org.eclipse.hawkbit.dmf.json.model.DownloadAndUpdateRequest, thingId=new_device}, delivery-mode=2, priority=0, correlation-id=null, reply-to=null, expiration=null, message-id=null, timestamp=null, type=null, user-id=null, app-id=null, cluster-id=null)

This could make believe that content-type, content-encoding,..... are "valid" AMQP properties, while in fact RabbitMQ states :

Invalid properties will be ignored. Valid properties are:

content_type
content_encoding
priority
correlation_id
reply_to
expiration
message_id
timestamp
type
user_id
app_id
cluster_id

Notice the difference between the dash (-) and the ('_underscore')

To avoid confusion, the java client should print the "official" property names using underscores.

Start in com.rabbitmq.client.impl.AMQContentHeader and inspect toString together with appendPropertyDebugStringTo. Update the displayed AMQP property names to use underscores rather than dashes, then verify the resulting output matches the official property names listed in the issue.