OK let me answer myself, maybe someone will find this useful when experimenting with the new features.
Graphql plugin can be installed via CLI using this command:
npm run strapi install graphql
Anyway this takes me to another question: when I query a collection via graphql, I can now get the total count of records in the ResponseCollectionMeta field. Cool, thanks for that!
But - when there is a relation type field, it returns different type (RelationResponseCollection), which doesn’t have any kind of meta datatype, thus it’s impossible to get the related records count OOTB.
Is there a plan to implement this in v4?