feat(google): Handle custom compute instances

[7onn]

Work in progress

Why is this PR necessary? In order to provide the pricing for GCP custom instances (e.g custom-20-20480),, we need to adapt the attribute filters not to search by machine type but by the amount of CPU and RAM specified.

The first draft of this PR only comprehends the pricing for GKE node pools but the idea is to extend this to every compute engine resource.

What does it do? This PR creates a new function customComputeCostComponent similar to computeCostComponent. Also, it adds a condition verifying whether the node pool employs a custom machine type or not.

References: https://github.com/infracost/infracost/issues/1447