chore: [DevOps] Add PMD rules for public API exposure of model types

[Jonas-Isr]

Context

This PR introduces new PMD rules to check whether code from .model packages get exposed in public API.

It flags the following:

• non-beta public methods that return or accept types from .model package,
• non-beta public classes extending .model types,
• non-beta public Lombok @with annotations on fields with .model types,
• non-beta public Lombok @Getter/@Setter/@Value/@DaTa on fields with .model types.

Warnings about current violations of these rules are suppressed.

Feature scope:

• add above rules to PMD
• suppress warnings on currently released code

Definition of Done

• Functionality scope stated & covered
• Tests cover the scope above
• Error handling created / updated & covered by the tests above
• Aligned changes with the JavaScript SDK
• Documentation updated
• Release notes updated

[newtork]

Looks good to me.
I would say let's try it out! If we encounter false-positives or decide to no longer care - we can still remove the pmd rule without issues.