feat(message queue): Message queue documents

[Meggielqk]

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[Copilot]

Pull Request Overview

This PR introduces comprehensive documentation for the Message Queue feature in EMQX 6.0. The documentation covers conceptual explanations, practical usage guides, and quick start tutorials across English, Chinese, and Japanese languages.

Key changes in this PR:

• Adds complete Message Queue documentation with concept explanations, user guides, and quick start tutorials
• Updates the messaging introduction pages to reference the new Message Queue feature
• Adds navigation structure for Message Queue documentation in the directory configuration

Reviewed Changes

Copilot reviewed 14 out of 20 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
zh_CN/messaging/introduction.md	Updates Chinese messaging introduction to include Message Queue as an extended MQTT feature
zh_CN/message-queue/*.md	Adds comprehensive Chinese documentation for Message Queue concepts, usage guide, and quick start tutorial
ja_JP/message-queue/*.md	Adds Japanese documentation for Message Queue user guide, quick start, and concepts
en_US/messaging/introduction.md	Updates English messaging introduction to include Message Queue documentation
en_US/message-queue/*.md	Adds complete English documentation for Message Queue feature
zh_CN/dashboard/cluster_settings.md	Minor update to cluster description functionality
en_US/dashboard/cluster_settings.md	Minor update to cluster description functionality
dir.yaml	Adds Message Queue section to documentation navigation structure

Comments suppressed due to low confidence (2)

zh_CN/message-queue/message-queue-task.md:1

• The explanation of message.key is inconsistent. The text states it extracts from the client ID of the message publisher, but message.key typically refers to a message property, not the client ID. This should be clarified or corrected to match the actual implementation.

# 消息队列用户指南

---

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[savonarola]

Nit: we better remove

• "[MQ subscription registry]"
• "via emqx_ds_client"
  strings from the pic: they are related to very internal details

[savonarola]

Maybe give somewhere an example of the context on which the expression is evaluated.
In json form:

{
  "message": {
    "qos": 0,
    "topic": "some/topic",
    "payload": "some-payload",
    "headers": {
      "client_attrs": {},
      "proto_ver": 5,
      "properties": {
        "User-Property": {
          "user-prop": "some-value"
        }
      },
      "peerhost": "127.0.0.1",
      "username": "undefined",
      "protocol": "mqtt",
      "peername": "127.0.0.1:49352"
    },
    "from": "clientid",
    "timestamp": 1759238376252,
    "id": "..non utf8 bytes...",
    "flags": {
      "retain": false,
      "dup": false
    },
    "extra": {}
  }
}

As Erlang term:

#{message =>
      #{extra => #{},
        flags => #{dup => false,retain => false},
        id => <<0,6,64,4,154,125,229,77,244,69,0,0,28,21,0,2>>,
        timestamp => 1759238376252,from => <<"clientid">>,
        headers =>
            #{peername => <<"127.0.0.1:49352">>,protocol => mqtt,
              username => undefined,peerhost => <<"127.0.0.1">>,
              properties =>
                  #{'User-Property' => #{<<"user-prop">> => <<"some-value">>}},
              proto_ver => 5,client_attrs => #{}},
        payload => <<"some-payload">>,topic => <<"some/topic">>,
        qos => 0}}

[savonarola]

Also IMO we may link the word "Expression" when we mention it to the variform docs, so that a reader could easily get the syntax of the expressions.

[id]

Let's do it tomorrow.