Relationship!(r1::T, r2::R; context::Module)::AbstractModel where {T<:AbstractModel, R<:AbstractModel}

julia> Base.@kwdef mutable struct Role <: AbstractModel
         id::DbId = DbId()
         name::String = ""
       end
julia> Role(name::Union{String,Symbol}) = Role(name = string(name))


julia> Base.@kwdef mutable struct Permission <: AbstractModel
         id::DbId = DbId()
         name::String = ""
       end
julia> Permission(name::Union{String,Symbol}) = Permission(name = string(name))


julia> Relationship!(user, role)

julia> isrelated(role, permission)