[module-sdk] warn not error on missing certificate secret

[diyliv]

Summary

• Fix regression in copy-custom-certificate hook: when the configured secretName does not exist in the cluster, the hook now logs a Warn and sets placeholder values ("<none>") instead of returning a hard error.
• Why: in the original go_lib implementation this was a warning with fallback, but the module-sdk port incorrectly changed it to errors.New() — causing infinite hook retries that block the parallel queue and prevent other modules from starting.
• Affected files: common-hooks/copy-custom-certificate/hook.go, common-hooks/copy-custom-certificate/hook_internal_test.go.

Context

When a user configures https.mode: CustomCertificate with a secretName, the secret might temporarily not exist (cert-manager not yet created, rotation in progress, etc.). The original go_lib hook handled this gracefully — warn + fallback values + continue. The module-sdk version returned an error, which caused:

• Hook failures with failures 2316 (endless retries)
• Blocked parallel queue — other hooks and modules stuck
• Certificate not distributed across namespaces

This fix aligns module-sdk behaviour with the original go_lib implementation.

Example

Before (broken):

ModuleHookRun:...:custom_certificates:OperatorStartup:failures 2316:
module hook failed: custom certificate secret name is configured,
but secret with this name 'ngkcore-com-wildcard-tls' doesn't exist

→ queue status: sleep after fail, other modules blocked.

After (fixed):

WARN: custom certificate secret name is configured, but secret with this name doesn't exist secret_name=ngkcore-com-wildcard-tls

→ queue status: sleep, values set to <none> placeholders, other modules proceed normally.