Added node pool name validation

[akijakya]

Q	A
Bug fix?	no
New feature?	yes
API breaks?	no
Deprecations?	no
Related issues	fixes #2622
License	Apache 2.0

What's in this PR?

Adding validation for node pool names (only accept lowercase characters and numbers) for clusters created on AWS.

Why?

The eks-create-asg Cadence workflow errors if there are special characters because the node pool name gets attached to the stack name; also the configure-nodepool-labels workflow errors if there are uppercase characters in the nood pool name resulting in unsuccessful cluster creation, so it is useful if a validator catches these cases even before the cluster creation begins.

Additional context

Example config.yaml:

{
  "cloud": "amazon",
  "location": "eu-west-1",
  "name": "test-validation",
  "properties": {
    "eks": {
      "nodePools": {
        "pool1X": {
          "autoscaling": true,
          "count": 5,
          "instanceType": "t3a.small",
          "maxCount": 10,
          "minCount": 2
        }
      },
      "version": "1.20"
    }
  },
  "secretName": "secret_name"
}

Response (banzai CLI):

ERRO[0013] failed to create cluster: 400 Bad Request (err pipeline.GenericOpenAPIError, request=map[cloud:amazon location:eu-west-1 name:test-validation properties:map[eks:map[nodePools:map[pool1X:map[autoscaling:true count:5 instanceType:t3a.small maxCount:10 minCount:2]] version:1.20]] secretName:secret_name], response={"code":400,"message":"node pool name 'pool1X' invalid: a DNS-1123 subdomain must consist of lower case alphanumeric characters","error":"node pool name 'pool1X' invalid: a DNS-1123 subdomain must consist of lower case alphanumeric characters"}
)
Error: failed to create cluster: 400 Bad Request
failed to create cluster: 400 Bad Request

Checklist

• Implementation tested (with at least one cloud provider)
• Code meets the Developer Guide
• [] OpenAPI and Postman files updated (if needed)
• [] User guide and development docs updated (if needed)
• [] Related Helm chart(s) updated (if needed)