feat(mqtt source, mqtt sink): add MQTT v5 protocol support

[vitalvas]

Summary

• Add MQTT v5 protocol support to the mqtt source and mqtt sink, selectable via a new protocol_version option (defaults to v311 for backward compatibility).
• Expose v5 publish properties (payload format indicator, message expiry, topic alias, response topic, correlation data, content type, user properties) on the sink under a new publish_properties config section, and surface incoming v5 properties as source event metadata.
• Add end-to-end acknowledgements to the mqtt source: when enabled, the source switches to MQTT manual ack mode and only sends PubAck to the broker once Vector has delivered the event downstream, providing at-least-once semantics for both v3.1.1 and v5.
• Derive the sink's accepted input types from the configured encoder so logs, metrics, and traces are all transportable over MQTT (default json encodes all three; use native_json for lossless Vector-to-Vector p ipelines). Mis-routed event types are now rejected at config build time instead of silently dropped by the codec.
• Emit open_connections and connection_shutdown_total telemetry from both source and sink, plus richer component_errors_total coverage for connection, subscribe, and acknowledgement failures.
• Consolidate the v3 and v5 connection-building code into a shared common::mqtt::build_connector to keep the source and sink in sync.

Vector configuration

sources:
  my_mqtt_source:
    type: mqtt
    host: "mqtt.example.com"
    port: 1883
    topic: "events/#"
    protocol_version: v5
    acknowledgements: true
    connect_properties:
      session_expiry_interval: 300

sinks:
  my_mqtt_sink:
    type: mqtt
    inputs: ["my_mqtt_source"]
    host: "mqtt.example.com"
    port: 1883
    topic: "events/{{ .namespace }}"
    protocol_version: v5                                                                                                                                                                                                  publish_properties:
      content_type: "application/json"
      message_expiry_interval: 3600
      user_properties:
        source: vector
    encoding:
      codec: json

How did you test this PR?

• New unit tests for connector building (v3/v5, manual_acks propagation, credential and client_id validation), publish-property conversion (all fields, boundary values), QoS conversions, source metadata application (v3 and v5, all 7 v5 fields, no-op on non-log events), and direction tagging on connection errors. 25 mqtt unit tests pass.
• Existing v3.1.1 integration tests continue to pass.
• Manual verification that the default protocol_version remains v311 and existing configurations behave unchanged.

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

Notes

• Please read our Vector contributor resources.
• Do not hesitate to use @vectordotdev/vector to reach out to us regarding this PR.
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  • Alternatively, we recommend running the following locally before pushing to the remote branch:
    • make fmt
    • make check-clippy (if there are failures it's possible some of them can be fixed with make clippy-fix)
    • make test
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• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
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[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[chatgpt-codex-connector]

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Reviewed commit: 9cd665493e

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[vitalvas]

I have read the CLA Document and I hereby sign the CLA

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 3fcb871c61

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[vitalvas]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 👍

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• Open a pull request for review
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[rtrieu]

some minor suggestions to comply with our style guide

[vitalvas]

@rtrieu Thanks for the suggestions. Applied them in eee8b3e