Documentation: Educate about idempotency of user-defined functions

[amotl]

About

@gsaviane suggested to improve the documentation a bit. Thank you!

Preview

• https://mqttwarn--714.org.readthedocs.build/configure/transformation.html#user-defined-functions

References

• Messages directed only to the first target when a format function is defined #690 (comment)

[coderabbitai]

Important

Review skipped

Auto reviews are limited based on label configuration.

🏷️ Required labels (at least one) (1)

• coderabbit-review

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5a5a4ea3-067f-4a26-852b-ba17125f9960

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

_{Comment @coderabbitai help to get the list of available commands.}