Add note to trigger and scheduler regarding missing information

[MrGeneration]

In some situations it's possible that trigger conditions can't be fullfilled. One of the main reasons for such a situation would be missing information in that situation.

As example: If you tell Zammad to check for article based information but do not add an article to that ticket, a trigger can't fire at that moment. The condition simply never can be met.

This technically affects schedulers and triggers and is very situation specific, but is worth mentioning in the docs.

[MrGeneration]

As for triggers this is mentioned in Limitations by now: https://admin-docs.zammad.org/en/latest/manage/trigger/limitations.html