Unify dimensions GraphQL API across Program V2 and Forms V2

[japsu]

While the Dimension and DimensionValue models are already unified across Program V2 and Surveys V2, so far they have used their own GraphQL APIs. This combines GraphQL query types and mutations for those.

There is a new event(…).universe(…).dimensions GraphQL API; however, that is intended only for directly interacting with dimensions and you will mostly continue using the dimensions through event(…).program.dimensions and event(…).forms.survey(…).dimensions.