[feat] validate kubernetes namespace

[schwichti]

Error: metadata.0.name a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is 'a-z0-9?(.a-z0-9?)*')
│
│ with module.simphera.module.simphera_instance["next"].kubernetes_namespace.k8s_namespace,
│ on .terraform\modules\simphera\modules\simphera_aws_instance\k8s.tf line 5, in resource "kubernetes_namespace" "k8s_namespace":
│ 5: name = var.k8s_namespace