feat(helm-chart): support initContainers override

[wengyao04]

feat(helm): support initContainers in deployment template

This PR adds support for initContainers in the kubernetes-mcp-server Helm chart.

Users can now define fully customizable init containers via .Values.initContainers, which are rendered using tpl to allow
templating within container specs.

Highlights:

• Introduces initContainers in values.yaml (default empty list)
• Renders initContainers before main containers in the pod spec
• Maintains backward compatibility (no behavior change by default)

This allows workloads to perform pre-start initialization steps (e.g., config generation, secret preparation, data migration)
without forking or patching the chart, and users can use k8s native sidecar containers.

[matzew]

Code review

Found 1 issue:

1. Missing helm-docs update — The PR adds initContainers to values.yaml but does not regenerate charts/kubernetes-mcp-server/README.md. A check-helm-docs CI job (added in feat: Add helm docs ci check and regenerate docs #798) validates that README.md is up-to-date by running make helm-docs and checking for uncommitted changes. This check will fail for this PR.

kubernetes-mcp-server/charts/kubernetes-mcp-server/values.yaml

Lines 169 to 179 in ce0728f

	# -- Init containers to run before the main container starts.
	# -- Each container is defined as a complete container spec.
	# -- Supports tpl for templating.
	initContainers: []
	# - name: init-config
	# image: busybox:latest
	# command: ["sh", "-c", "echo 'Preparing config...' && cp /defaults/* /config/"]
	# volumeMounts:
	# - name: config-volume
	# mountPath: /config

Run make helm-docs locally and commit the updated charts/kubernetes-mcp-server/README.md before merging.

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