feat: Support for GKE private clusters without default node pool

[ciroclover]

Fixes #2407

The diff shows a massive difference due to the "dynamic" block indentation.

The changes are:

• Ensure that we define the initial_node_count when is not defined in the node-pool [ref].
• Make the node-pool block dynamic. Add the conditional to ensure that the block is not generated when node_pools = [] [ref]
• Fix the cluster_name variables in the main.tf. I honestly believe that we could just use cluster_name_computed = var.name, however, more tests should be needed. [ref]

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[m0ps]

@ciroclover, I think, in such an arrangement, it would never be accepted. First of all, you have to use autogen to generate all submodules automatically. Also, don't forget to generate docs and perform proper linting... I would recommend you make yourself familiar with the contribution guide