docs: update Coder version in Kubernetes doc (#16658)

closes #16570 

thanks @Cjkjvfnby !


@matifali I think there is/was an automation, but I'm not sure if it's
been dropped. `kubernetes.md` has:

```md
<!-- autoversion(mainline): "--version [version]" -->
...
<!-- autoversion(stable): "--version [version]" -->
```

~additionally, I removed the `## Prerequisites` section from
`kubernetes-logs.md` because if it's only a requirement for Coder
versions earlier than 0.28.0, it's probably more confusing than useful
to the majority of readers.~

---------

Co-authored-by: M Atif Ali <atif@coder.com>

docs/install/kubernetes.md

@@ -129,7 +129,7 @@ We support two release channels: mainline and stable - read the
   helm install coder coder-v2/coder \
       --namespace coder \
       --values values.yaml \
-      --version 2.18.0
+      --version 2.19.0
   ```
 
 - **Stable** Coder release:
@@ -140,7 +140,7 @@ We support two release channels: mainline and stable - read the
   helm install coder coder-v2/coder \
       --namespace coder \
       --values values.yaml \
-      --version 2.17.2
+      --version 2.18.5
   ```
 
 You can watch Coder start up by running `kubectl get pods -n coder`. Once Coder