Add tags mq.message.keys and mq.message.tags for RocketMQ producer span

[nisiyong]

RocketMQ message has tags and keys concept.
See https://rocketmq.apache.org/docs/4.x/producer/04concept1#message

• Add span tag message.tags to help developers identify messages.
• Add span tag message.keys to help developers search messages by key in the RocketMQ console.

• Update the CHANGES log.

[wu-sheng]

Isn't keys enough to locate the message? The tracing should take as less messages as possible

[nisiyong]

Isn't keys enough to locate the message?

The keys is indeed enough to locate the message, which is convenient for locating the problem of message loss.
The tags is used to distinguish interrelated messages under the same topic, it is convenient for identifying what type of messages are produced, and the consumer side will filter message with tags, which is useful to help developers know the subscription between provider and consumer, not only topic name. For more explanations see: https://rocketmq.apache.org/docs/4.x/producer/04concept1/#when-to-use-topictag

The tracing should take as less messages as possible

It should follow this principle, now these tags will be ignored when they are blank.