Add cluster-level variable max_pods as defaults value for node pools

[niccoloraspa]

I believe that it would be useful to specify a cluster-level variable max_pods that act as default values for the node pools.

This value can be overwritten by the node_pools if necessary.

module "eks" {
  source          = ....
  cluster_name    = ...
  max_pods        = 100
  node_pools = [
    {
      name          = "infra"
      # ...
      # I will use `max_pods` = 100
    },
    {
      name          = "app"
      max_pods  = 10 # I will not use the default value
    },
  ]
}

I think the same approach can be followed for other variables if necessary.

As an example, each node_pool expects a tags variable that if not specified results in error.
I think this is cumbersome; we need to repeat (possibly) the same tags to all the node pools.
We could also promote the tags variable at the cluster level and have node pools inherit this value.

[angelbarrera92]

I think it could make sense :) every variable has to be carefully reviewed, but in the end, I like the concept!