[dmt] fix helmignore missing chart dirs

[diyliv]

Summary

• Add monitoring/ to moduleTemplateExclude: the monitoring/ directory contains Grafana dashboards and Prometheus rules that are rendered by Helm templates. It MUST be in the chart — listing it in .helmignore would break the module.
• Clearer comments on moduleTemplateExclude grouping: "required by Helm" vs "read by Deckhouse directly".
• Updated unit tests: added test for monitoring/ being skipped, added test verifying that only templates/, charts/, monitoring/ are exempt from .helmignore (other dirs like docs/, crds/, hooks/, openapi/ correctly require .helmignore entries).

Context

The checkModuleRootCoverage check scans the module root and warns about any file/directory not listed in .helmignore — except those in moduleTemplateExclude. The exemption list was missing monitoring/, causing false warnings:

WARN Directory 'monitoring/' is not listed in .helmignore

monitoring/ is referenced by templates/monitoring.yaml via helm_lib_prometheus_rules_recursion and helm_lib_grafana_dashboards_recursion. Adding it to .helmignore breaks chart rendering.

Directories like docs/, crds/, hooks/, openapi/ correctly trigger warnings — Deckhouse reads them directly from the module filesystem, not from the rendered Helm chart. They should be in .helmignore to keep the chart lean.

Example

Before (false warning):

WARN Directory 'monitoring/' is not listed in .helmignore

After:

(monitoring/ is skipped — needed for chart rendering)
(successful lint)