feat: add diagnostic hint log when driver cannot reach kube-apiserver on startup

[pujitha24]

/kind feature

What this PR does / why we need it:

Motivation:
When the driver fails to start because it cannot reach the kube-apiserver
(e.g. RESTMapper/discovery client construction in ctrl.NewManager, or cache
sync in mgr.Start failing due to DNS, connection refused, or timeouts), the
existing logs ("failed to start manager", "failed to run manager") give no
hint about the likely root cause. Issue #1753 reports exactly this: a driver
pod failed to initialize with only a generic wrapped error, with no guidance
that network connectivity to the kube-apiserver should be checked.

Approach:
Add an isNetworkError helper in cmd/secrets-store-csi-driver/main.go that
classifies an error as network-related if it unwraps to a net.Error (covers
*net.DNSError, *net.OpError, etc.) or its message contains one of a small
set of well-known connectivity failure substrings ("connection refused", "no
such host", "i/o timeout", "context deadline exceeded"). When this helper
returns true at the two manager-startup failure points, an additional
klog.ErrorS call logs: "the driver is unable to communicate with the
kube-apiserver, check network connectivity between the node and the
kube-apiserver". This mirrors the existing isMaxRecvMsgSizeError pattern in
pkg/secrets-store/provider_client.go.

This change is purely additive: it does not alter control flow, return
values, exit codes, or any existing log message. The original error is still
logged and returned/panicked exactly as before; only an extra diagnostic log
line is emitted when the error looks network-related. User-visible behavior
(pod restarts on manager start failure) is unchanged before/after this fix —
the benefit is a clearer, more actionable log line for operators debugging a
non-starting driver pod, not a change in recovery behavior.

Validation:

• go build ./... passes.
• go test ./cmd/... -v passes, including the new table-driven
  TestIsNetworkError covering nil errors, unrelated errors, wrapped
  net.DNSError, and each of the matched substring cases.
• gofmt -l and go vet ./cmd/... report no issues.

Fixes #1753

Signed-off-by: Pujitha Paladugu 10557236+pujitha24@users.noreply.github.com

[kubernetes-prow]

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[kubernetes-prow]

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[kubernetes-prow]

Hi @pujitha24. Thanks for your PR.

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[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: pujitha24
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[Copilot]

Pull request overview

This PR improves startup troubleshooting by emitting an additional, actionable log hint when the driver appears unable to communicate with the kube-apiserver during manager initialization or startup, helping operators diagnose common node→apiserver connectivity failures.

Changes:

• Added isNetworkError in cmd/secrets-store-csi-driver/main.go to classify likely kube-apiserver connectivity-related startup errors.
• Emitted an extra klog.ErrorS hint at both manager construction and manager start failure points when isNetworkError matches.
• Added a table-driven unit test for isNetworkError.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
cmd/secrets-store-csi-driver/main.go	Adds network-error classification and an extra diagnostic hint log on manager startup failures.
cmd/secrets-store-csi-driver/main_test.go	Adds unit tests covering isNetworkError classification behavior.

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