Improve/Rewrite the DMN reference docs

[saig0]

Description

The DMN reference docs were mainly copied from C7. We can improve the DMN docs to guide the users better on how to model DMNs.

Possible action items:

• update the screenshots of the modeler
  • the screenshots show an older version of the modeler
• explain how access the result of required decisions
  • more details and examples
• explain the structure of the decision results
  • the decision result depends on the decision type
  • the decision result is different for decision tables based on the hit policy and outputs
• remove XML snippets
  • XML snippets are not relevant for users
  • attributes in the XML are not relevant as well
• align DMN examples for C8
  • for example, a literal expression can't invoke methods on a bean
• improve the linking to FEEL
  • more examples of common FEEL expressions
  • especially for input entries, but also for input expressions and output entries
• focus on how users model a DMN
  • align the structure on the user flow
  • first, start with a DRG
  • then, create a decision
  • set a decision id and name
  • select the decision type that is suitable *
  • then, optionally, define input data
  • next, define the logic of the decision
  • ...

Related issues:

422

823

834

[menski]

We could also think about applying similar improvements to the BPMN docs, focusing more on the user perspective then the technical perspective. Seems to be a bigger task, which needs a general restructuring of the structure.

[akeller]

Added the component:zeebe label for hygiene since I see this is in the ZPA backlog already. Please reach out if you'd like additional support from the DevEx team.