docs: Review authentication docs in ecosystem

Review existing state of authentication docs across wpgraphql.com and [wp-graphql-headless-login](https://github.com/AxeWP/wp-graphql-headless-login) to see where we can add clarity. 

Evaluate the role of [wp-graphql-jwt-authentication](https://github.com/wp-graphql/wp-graphql-jwt-authentication) in the ecosystem and see if its needed.