Reorder custom_nodepool_arguments for node-pool create command

[scaliby]

Fixes / Features

As node-pool create user-provided arguments are not appended as latest to the underlaying command execution, it is impossible to override the ones that appended by the code later. For gcloud command execution order matters and even if argument is duplicated, the later one wins. By moving custom_nodepool_arguments at the very end, we are allowing users to override all pre-generated arguments.

For instance, to override a default nodepool version argument used by XPK, we can supply an argument:
--custom-nodepool-arguments="--node-version=1.33.3-gke.1255000"
This will render command:

gcloud beta container node-pools create xpk-test-v6e-1x1-3-np-0 
  // arguments
  --node-version=1.33.3-gke.1136000 // the default one that XPK is using
  --node-version=1.33.3-gke.1255000 // the one from override

This will result with nodepool created with 1.33.3-gke.1255000 version, as gcloud picks the value from last argument of any given name.

Testing / Documentation

Tested with command:
python3 xpk.py cluster create --cluster=xpk-test-v6e-1x1-3 --project=tpu-staging-env-one-vm --tpu-type=v6e-1x1 --zone=us-central1-b --num-nodes=1 --enable-autoprovisioning --on-demand --custom-nodepool-arguments="--node-version=1.33.3-gke.1255000"

• [y] Tests pass
• [y] Appropriate changes to documentation are included in the PR

[RoshaniN]

Thanks!

While this looks like an acceptable change, I'm curious to know how this would make a difference to the overriding behavior of gcloud arguments. Is there a bug / example you could share to aid the PR description?

[scaliby]

@RoshaniN added more verbose description