Add "permissions" to the Community, so it is abstracted from Keycloak

[guillecro]

We will add the field permissions to define a set of key-value attributes as permissions: So it would be:

{
  (...)
  permissions:  {
    user: { }
    accountable: {
      documentCreationLimit: 1
    }
    admin: { }
  }
}

[guillecro]

Added in #61