[kubernetes] Change settings coredns replicas and image (#1410)

Signed-off-by: Andrei Kvapil <kvapss@gmail.com>

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## What this PR does


### Release note

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```release-note
[]
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## Summary by CodeRabbit

- New Features
- Exposed configuration for CoreDNS: you can now set the image
repository and replica count via values.
- Changes
- CoreDNS now deploys in the kube-system namespace for better alignment
with cluster services.
- Default CoreDNS replica count increased to 2 to improve availability.

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packages/system/coredns/Makefile

@@ -1,5 +1,5 @@
 export NAME=coredns
-export NAMESPACE=coredns
+export NAMESPACE=kube-system
 
 include ../../../scripts/package.mk
 

packages/system/coredns/values.yaml

@@ -0,0 +1,4 @@
+coredns:
+  image:
+    repository: registry.k8s.io/coredns/coredns
+  replicaCount: 2