Implement role based access control (RBAC)

[he-james]

Description
A lot of different kinds of people will be using our service. As a result,
role based authorization is absolutely necessary for this product. Follow the
NestJS docs on RBAC to do this https://docs.nestjs.com/security/authorization

UC

• As a user, I want to see only the information relevant to my
  position or role from the Nexus in order to use it in a clear manner.

AC

• GET routes must exist that, when requested, will respond only with data for
  the respective role.