Plugins: Formatieren von Payloads per jq

[doits]

Fix #20501

Erster Versuch, erst mal nur im MQTT-Plugin.

Achtung: Das erste Mal, dass ich Go-Code umbaue bzw. in Go programmiere. Anfängerfehler vorprogrammiert, was vielleicht auch die nachfolgenden Fragen zeigen.

Fragen:

• Wie kann man das grundsätzlich testen, ohne dass gleich ein echter MQTT-Server im Hintergrund laufen muss?
• Kann man das mit weniger Änderungen testen, ohne das MQTT-Plugin nur wegen des Tests so zu refactoren?
• Aktuell wird die neue FormatPayload-Funktion getestet (die gibt es eigentlich nur, damit man sie im Test nutzen kann 😅 ), aber eigentlich wäre es besser zu testen, was am Ende zu m.client.Publish gesendet wird – also was letztendlich "rausgeht". Sehe aktuell nicht, wie man das m.client.Publish im test mocken könnte, damit man dort das payload rausfischen kann.

Ich denke ich brauche etwas Hilfe/Denkanstöße von erfahrenen Programmieren, damit ich hier sauber weiterkomme. Gebt gerne kritisches Feedback und/oder ein paar Hinweise, wie ihr es angehen könntet.

Summary by Sourcery

Introduce payload formatting using jq in the MQTT plugin and refactor publishing logic.

New Features:

• Allow formatting MQTT message payloads using jq expressions before publishing.

Enhancements:

• Refactor MQTT publishing logic into reusable FormatPayload and Publish methods.

Tests:

• Add a unit test for the new jq payload formatting functionality.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request introduces payload formatting using jq for the MQTT plugin. It refactors the existing setter functions to use a new Publish helper function, which in turn calls a new FormatPayload function to process the payload using a jq pipeline if configured. A new test is added to verify the FormatPayload functionality.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Introduce new helper functions for formatting and publishing payloads.	Add FormatPayload function to process the payload using a jq pipeline. Add Publish function to format and publish a value to the topic.	plugin/mqtt.go
Refactor setter functions to use the new Publish helper.	Update IntSetter to call m.Publish. Update FloatSetter to call m.Publish. Update BoolSetter to call m.Publish. Update StringSetter to call m.Publish.	plugin/mqtt.go
Add a new test for the FormatPayload function.	Add TestFormatPayload to verify payload processing with a jq expression.	plugin/mqtt_test.go

Possibly linked issues

• Plugins: Anpassung des Payloads per JQ #20501: The PR adds the ability to use jq to format/modify the payload before publishing to an MQTT topic, as requested in the issue.

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[andig]

Wäre es nicht einfacher und weniger diff gewesen, diesen Schritt in setFormattedValue mit einzubauen? Es muss ohnehin auch analog für http, script etc erfolgen.