create user, superhero, agent entities with relations

[championswimmer]

this issue is only for entities, do not make controller/service/api stuff for this issue yet. just the TypeORM entities.

[prathambatra]

@championswimmer working on this. can you tell required fields for admin?

[championswimmer]

https://github.com/coding-blocks/wakanda-backend/wiki/Entities

[championswimmer]

@prathambatra you working on this ?

[prathambatra]

@championswimmer I will make PR by tomorrow