[Sample] Create Simple plugin to store Post

[kesslerdev]

Entities

create a sample for a blog,

• Post Entity (persisted) with all needed for save update etc
• Category Entity (also persisted) related to posts

all of these entities have basic fields name img content ...

What for ?

first, have a sample for newbees
second test the implementation of graphcool order, filtering & pagination
see docs for how implement in graphql

https://www.graph.cool/docs/reference/relay-api/ordering-by-field-sa8aiwurae
https://www.graph.cool/docs/reference/relay-api/filtering-by-field-aephaimu5n
https://www.graph.cool/docs/reference/relay-api/pagination-riekooth4o

same api that SecureField but with SecureListField or ListField (field with no params that return IEnumerable)

return Field with all needed params without specify return entire list