docs(troubleshooting): fix KubeOVN MASTER_NODES example path and key (#483)

## What

Fixes the KubeOVN Not Scheduling troubleshooting example in
`content/en/docs/v1/install/kubernetes/generic.md`:

- The key was `kube-ovn` with a dash, but the field in
`packages/core/platform/values.yaml` is
`networking.kubeovn.MASTER_NODES` — no dash. A reader copying the old
block ended up with a value block that matched nothing in the platform
schema.
- The YAML sketch was also missing `apiVersion` / `kind` / `metadata`,
so it was not obvious which Package it was meant to patch. Rewrite the
example as a full `cozystack.cozystack-platform` manifest that matches
the documented path in the Platform Package reference, and add a
cross-reference to that reference entry.

## Why

Reported in the community chat:

> в вельюсах платформы на гите `kubeovn:`  
> а в доках в траблшутинг разделе `kube-ovn:`

The typo was a drift between the `packages/core/platform/values.yaml`
schema (where the field is `networking.kubeovn.MASTER_NODES`) and this
troubleshooting example. The Platform Package reference
([`operations/configuration/platform-package.md`](content/en/docs/v1/operations/configuration/platform-package.md))
already uses the correct `kubeovn` form, so the troubleshooting example
was the odd one out.

## Verification

- Checked the target field name against
`packages/core/platform/values.yaml` in upstream `cozystack/cozystack`:

  ```yaml
  networking:
    ...
    kubeovn:
      MASTER_NODES: ""
  ```
- Confirmed that
`content/en/docs/v1/operations/configuration/platform-package.md`
already documents the same key path (`networking.kubeovn.MASTER_NODES`),
so the fix aligns with the existing reference.
- `hugo` builds cleanly; the troubleshooting section renders with the
corrected manifest.

## Out of scope

`content/en/docs/v1/install/how-to/kubespan.md` still uses `kube-ovn:`
under `spec.components.networking.values` for an MTU override. That
example needs its own verification pass against upstream chart values
(`mtu` is not in `packages/system/kubeovn/charts/kube-ovn/values.yaml`
at all, so it may already be stale) and is left for a follow-up.

Author: kvaps

content/en/docs/v1/install/kubernetes/generic.md

@@ -435,14 +435,25 @@ This example uses k3s default CIDRs. Adjust for kubeadm (`10.244.0.0/16`, `10.96
 **Solution**: Ensure your Platform Package includes explicit `MASTER_NODES` configuration:
 
 ```yaml
+apiVersion: cozystack.io/v1alpha1
+kind: Package
+metadata:
+  name: cozystack.cozystack-platform
 spec:
+  variant: isp-full-generic
   components:
-    networking:
+    platform:
       values:
-        kube-ovn:
-          MASTER_NODES: "<YOUR_CONTROL_PLANE_IP>"
+        networking:
+          kubeovn:
+            MASTER_NODES: "<YOUR_CONTROL_PLANE_IP>"
 ```
 
+The key is `kubeovn` (no dash), matching the field in
+`packages/core/platform/values.yaml` — see also
+[`networking.kubeovn.MASTER_NODES`]({{% ref "/docs/v1/operations/configuration/platform-package" %}})
+in the Platform Package reference.
+
 ### Cilium Cannot Reach API Server
 
 **Symptom**: Cilium pods in CrashLoopBackOff with API connection errors.