Added auth role guards to be used on routes

[aniketgargya]

Added a guard to be used for protected routes.

The database collection should be named roles and each document should take the following form:

{
  "_id": {
    "$oid": "649a380b3ccb62010eee8a49"
  },
  "email": "xxxxxxxx@illinois.edu",
  "role": "Admin"
}

Example usage of the guard is provided in the @Patch(':id') route.