Add meta fields to GraphQL model definitions

[filipmiik]

Fixes inconsistency in provided meta fields/properties between REST API and GraphQL API. Following properties are added to GraphQL model definitions:

• _state (Collection, Singleton, Tree)
• _o (Collection, Tree)
• _mby (Collection, Singleton, Tree)
• _cby (Collection, Singleton, Tree)
• _pid (Tree)

Context: https://discourse.getcockpit.com/t/help-where-to-find-relations-when-getting-content-item-of-type-tree/2450/4

[aheinze]

Hi 👋

Thank you for the contribution. May I ask you to put the _o attribute to the tree related array. It is only available in tree models.

Thanks!

[filipmiik]

Oh, sorry, thought it's available for all collections. Fixed :)

[aheinze]

Děkuji!

[filipmiik]

Danke auch! :)