fix: allow component to deploy correctly when create_namespace is false

[agfunderburg10]

Correct description and doc to match actual default value of create_namespace var

what

• changes value of kubernetes_namespace to consider the create_namespace variable value
• corrects doc and description to show default create_namespace value as true

why

The kubernetes_namespace value that is passed into the "cloudposse/helm-release/aws" module was set as join("", kubernetes_namespace.default.*.id). When create_namespace is false, this resource is never created, resulting in an error (example below) during deployment. My fix will simply use the variable kubernetes_namespace if create_namespace is false.

Error example:

module.metrics_server.helm_release.this[0]: Creating...
╷
│ Error: create: failed to create: an empty namespace may not be set during creation
│ 
│   with module.metrics_server.helm_release.this[0],
│   on .terraform/modules/metrics_server/main.tf line 65, in resource "helm_release" "this":
│   65: resource "helm_release" "this" {
│ 
╵
exit status 1