feat: Add PromptTemplate type (#5787)

* Flesh out PromptVersionTemplate type

* Return GraphQL objects with the correct type

* Use new types in node query

* Decouple pydantic models and gql types

* Rebuild gql schema

* Rework model names

* Update gql schema

* Propagate name into schema

* Incorporate feedback

* Update schema

* adjust UI to new schema

* cleanup

* Remove `hub` naming and clean up type annotations

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Co-authored-by: Mikyo King <mikyo@arize.com>