feat: add run_as_non_root=True to Kubernetes Starter template (#16512)

This document sounds like `run_as_non_root=True` should be enabled for
workspaces.

https://coder.com/docs/install/kubernetes#kubernetes-security-reference
> All containers must run as non-root user
>  - Control plane - ...
> - Workspaces - Workspace pod UID is [set in the Terraform template
here](f57ce97b5a/examples/templates/kubernetes/main.tf (L274-L276)),
and are not required to run as root.

Administrators of the Kubernetes of a cluster I am working on have added
a security check on it, and prevent creating pods, without
`run_as_non_root=True`. So, I need to set it every time I create a
template.

According to the docs used with `run_as_user=1000` it should not have
negative effects and could be safely added.
https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.26/

examples/templates/kubernetes/main.tf

@@ -278,8 +278,9 @@ resource "kubernetes_deployment" "main" {
       }
       spec {
         security_context {
-          run_as_user = 1000
-          fs_group    = 1000
+          run_as_user     = 1000
+          fs_group        = 1000
+          run_as_non_root = true
         }
 
         container {