Improve wording about additional costs for ingress on custom clusters

When adding applications to a custom cluster, there is a sentence about additional costs. This is a specific reference to GKE pricing, but the cluster can actually be any generic Kubernetes cluster.

Note: This will add some extra resources like a load balancer, which incur additional costs. See GKE pricing

We should improve the wording of the note to better explain this.

This will add some extra resources like a load balancer, which may incur additional costs depending on the hosting provider Kubernetes is installed on. If you are using GKE, you can [check the pricing here](https://cloud.google.com/compute/pricing#lb).

This note will be the same for both GKE and existing clusters. The link to GKE pricing should be preserved.