add pipeline route for mqttproxy

[suchen-sci]

This pr add Pipeline route for MQTTProxy and also make backend Kafka a MQTT filter.

New version yaml:
Now MQTTProxy can route MQTT packets to different pipelines based on the packet type. Currently support: Connect, Disconnect, Publish, Subscribe, Unsubscribe.

kind: MQTTProxy
name: mqttproxy
port: 1883
auth:
  - userName: test
    passBase64: dGVzdA==
  - userName: admin
    passBase64: YWRtaW4=
pipelines:
  - name: publish-pipeline
    packetType: Publish
  - name: connect-pipeline
    packetType: Connect

name: publish-pipeline
kind: Pipeline 
protocol: MQTT
flow:
  - filter: topicMapper
  - filter: kafka 
filters:
  - name: topicMapper
    kind: TopicMapper
    ...
  - name: kafka
    kind: Kafka
    backend: [":9093"]

[codecov-commenter]

Codecov Report

Merging #453 (5e38e91) into main (42801f2) will decrease coverage by 0.05%.
The diff coverage is 82.13%.

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
- Coverage   80.57%   80.52%   -0.06%     
==========================================
  Files          70       74       +4     
  Lines        8171     8353     +182     
==========================================
+ Hits         6584     6726     +142     
- Misses       1230     1261      +31     
- Partials      357      366       +9     

Impacted Files	Coverage Δ
pkg/object/mqttproxy/spec.go	100.00% <ø> (ø)
pkg/object/mqttproxy/topic.go	100.00% <ø> (ø)
pkg/object/pipeline/mock.go	80.64% <0.00%> (-6.32%)	⬇️
pkg/filter/topicmapper/topicmapper.go	48.64% <48.64%> (ø)
pkg/filter/kafka/kafka.go	62.90% <62.90%> (ø)
pkg/object/mqttproxy/broker.go	74.33% <78.37%> (-0.72%)	⬇️
pkg/filter/mqttclientauth/mqttauth.go	83.56% <83.56%> (ø)
pkg/object/mqttproxy/client.go	80.54% <85.71%> (+3.37%)	⬆️
pkg/filter/connectcontrol/connectcontrol.go	96.10% <100.00%> (ø)
pkg/filter/kafka/topic.go	100.00% <100.00%> (ø)
... and 7 more

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[zhao-kun]

Suggest change YAML formation to:

rules:
  - when:
      packetType: Publish
    pipleline: publish-pipeline

For now, we just support the packetType as the only condition to dispatch the data to the pipeline. In the future, we could add extra conditions in when, such as topic start with /root/*, etc...

substitute keyword pipelines to rules just in order to align the YAML contents to HTTPPipeline.

[suchen-sci]

updated!

[zhao-kun]

Overall, look good to me, except for decoupling the Kafka plugin

[zhao-kun]

I have some jobs that were suspended for the PR. @localvar please help review the PR and push forward the progress of the merging when you are free

[samutamm]

LGTM