feat(helm): expose readinessHAMaxLag for HA readiness catch-up gate

[robfrank]

Summary

• ArcadeDB #4846 adds SERVER_READINESS_HA_MAX_LAG (arcadedb.server.readinessHAMaxLag, default 100), gating /api/v1/ready on Raft log catch-up in addition to the existing leader-known check.
• Wires the new knob through as observability.health.readinessHAMaxLag, emitted alongside -Darcadedb.server.readinessRequiresHA=true (a no-op upstream unless that flag is set).
• No chart version bump: 26.7.1 hasn't been released yet, so this rides along in the same unreleased version as the observability feature (#4463) it extends.

Test plan

• helm unittest . — 164/164 passing (3 new cases: default emission, override, and absence when readinessRequiresHA is false)
• helm lint . — clean

[gemini-code-assist]

Code Review

This pull request introduces the observability.health.readinessHAMaxLag configuration parameter to the ArcadeDB Helm chart, allowing users to specify the maximum Raft log lag for a follower to be considered ready. The review feedback points out a potential issue where a null or omitted value could lead to invalid JVM arguments, and suggests a robust template condition to safely handle defaults while preserving 0 as a valid value.

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[gemini-code-assist]

If observability.health.readinessHAMaxLag is omitted or set to null in a user's custom values, rendering {{ $health.readinessHAMaxLag }} directly will result in an empty or <nil> value in the JVM arguments, which can cause startup or parsing failures. Additionally, using a simple default 100 helper would incorrectly override a valid 0 value (since 0 is falsy in Go templates). To handle this robustly, we can define a default fallback that preserves 0 as a valid lag limit.

- -Darcadedb.server.readinessHAMaxLag={{ if or $health.readinessHAMaxLag (eq $health.readinessHAMaxLag 0) (eq $health.readinessHAMaxLag 0.0) }}{{ $health.readinessHAMaxLag }}{{ else }}100{{ end }}