feat(gke-cluster-standard): Set optionnal default_node_pool configuration

[anthonyhaussman]

Description

Add the possibility to set and initialize a default_node_pool to correctly size GKE Control-Planes in a restoration process.

Explanation

As I understand the reason for disabling the creation of the default_node_pool is to take advantage of the gke-nodepool module, I want to give the option to add this node_pool with a specific size to size Control-Planes during a Disaster Recovery Plan using the GKE restoration features.

To add more details, in my test when I used the gke-nodepool to add a nodePool after the creation of the cluster and launch directly a restore process, this one failed due to the resize of Control-Plane by adding nodes.
This action can take a long time, around 45 minutes.

By setting the initial default_node_pool at the creation of the cluster, GKE Control-Planes do not need to resize and improve the restoration process time by a lot.

That's why I would like to add this option.

By default, it keeps the same behavior as before and does not create the default_node_pool.
Furthermore, a validation block has been added to force to set the initial_node_count if remove_pool has been disabled.

The option can be simply added by setting:

  default_node_pool = {
    remove_pool        = false
    initial_node_count = 12
  }

I hope to have been clear enough. 🙏

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

[ludoo]

Thanks for the thorough explanation, it kind of does make sense to me. @juliocc WDYT?

[juliocc]

TIL. Makes complete sense sense.