Change OASP templates to use IdReference<Entity> as Eto to Eto references

[maybeec]

Currently, we are using Long to express references between Eto's. The latest version of the OASP introduced a new type called IdReference<Entity> to express references between Eto's, which are more readable. This has to be adapted in the templates.

[github-actions[bot]]

Stale topic. Please negotiate closing or discussing the relevance of this ticket.