[improve][doc] Clarify the definition of message key (#15469)
[improve][doc] Clarify the definition of message key (#15469)


merlimat/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,massakam/pulsar,massakam/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,merlimat/pulsar,merlimat/pulsar,massakam/pulsar