Add @depends-on directive to allow definition of explicit dependencies

[beetlebugorg]

There are a few rare cases where Gyro cannot infer a dependency between two resources. To allow for this a @depends-on directive should be defined that lets users define dependencies.

In this example node group creation may fail if the nategateway and route tables already exist.

aws::eks-nodegroup frontend
    name: "frontend"
    cluster: $(aws::eks-cluster $project)
    node-role: $(aws::iam-role eks-node)

    @depends-on: $(aws::nat-gateway *)
    @depends-on: $(aws::route-table private*)
end

The directive takes either a single reference or a list of references.