fix: incorrect `node_pools` variable type

[michaellzc]

node_pool map is a mix of string, bool, and number. therefore, it is better to use map(any) to indicate its type

moreover, list(map(string)) is breaking the use of this module in cdktf.

cdktf infers the type of module options based on the provided variable type. in the generated code, it will produce []map[string]string for node_pools option, but we want []map[string]interface{} in order to pass correct value

e.g. initial_node_count is a number not string

│ Error: Incorrect attribute value type
│
│   on .terraform/modules/gke_self_15C14BFE/modules/beta-private-cluster/cluster.tf line 434, in resource "google_container_node_pool" "pools":
│  434:   initial_node_count = lookup(each.value, "autoscaling", true) ? lookup(
│  435:     each.value,
│  436:     "initial_node_count",
│  437:     lookup(each.value, "min_count", 1)
│  438:   ) : null
│     ├────────────────
│     │ each.value is map of string with 16 elements
│
│ Inappropriate value for attribute "initial_node_count": a number is required.

notes: this change is fairly safe and I did not run any integration test from this repo

[comment-bot-dev]

@michaellzc Thanks for the PR! 🚀
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