Make NodePool optional for LKE-E in python sdk

[rammanoj]

📝 Description

What does this PR do and why is this change necessary?

• Make node_pools argument in cluster_create optional for LKE-E clusters.

✔️ How to Test

What are the steps to reproduce the issue or verify the changes?

• Create a standard cluster with below code and ensure that it fails with valueError

from linode_api4 import LinodeClient
from linode_api4.objects import LKECluster, LKENodePool

# creating for a new pool
client = LinodeClient("<token>", "https://api.linode.com/v4beta")
cluster = client.lke.cluster_create(
    label="demo-lke-cluster-pythons",
    region="us-ord",
    kube_version="v1.32",  # optional but recommended
    tier="standard")
print(f"Created cluster with ID: {cluster.id}")

# Output:
(lke-tools) ➜  tmp_python python3 main.py
Traceback (most recent call last):
  File "/Users/rpotla/Desktop/Codebase/test/tmp_python/main.py", line 6, in <module>
    cluster = client.lke.cluster_create(
              ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rpotla/Envs/lke-tools/lib/python3.12/site-packages/linode_api4/groups/lke.py", line 124, in cluster_create
    raise ValueError("LKE standard clusters must have at least one node pool.")
ValueError: LKE standard clusters must have at least one node pool.

• Create a enterprise cluster with below code and ensure that if suceeds.

from linode_api4 import LinodeClient
from linode_api4.objects import LKECluster, LKENodePool

# creating for a new pool
client = LinodeClient("<token>", "https://api.linode.com/v4beta")
cluster = client.lke.cluster_create(
    label="demo-lke-cluster-pythons",
    region="us-ord",
    kube_version="v1.31.9+lke7",  # optional but recommended
    tier="enterprise")
print(f"Created cluster with ID: {cluster.id}")

# Outputs:
(lke-tools) ➜  tmp_python python3 main.py 
Created cluster with ID: 551042