Can ObjectId be used as GET-Parameter directly?

[fm3]

Many routes implementations in our backend start with ObjectId.fromString(aPassedIdString).
Maybe an implicit conversion can be done by play to directly support ObjectId as a GET parameter type?

If the returned error looks different then, we should check how the frontend displays it.

Should probably be tackled after #8075 to minimize merge conflicts

Since ObjectId is moved to util or datastore there anyway, we should also use it everywhere in datastore/tracingstore where objectIds are handled (currently they are only passed around as strings there in some places)

[MichaelBuessemeyer]