docs: add CustomHealth Lua authoring guide - #617

Greptile Summary

Adds an example-first guide for authoring deployment-operator CustomHealth Lua scripts and registers it in documentation navigation and generated routes.

• Documents the CustomHealth manifest and Lua input/output contract.
• Lists supported health statuses and helper functions.
• Adds the new page beneath the deployment-operator section.

Confidence Score: 4/5

The documentation should not merge until the Lua input global is corrected, because copying the primary example currently produces a runtime script failure.

The guide consistently dereferences lowercase obj, but the operator registers uppercase Obj; Lua identifiers are case-sensitive, so the documented script indexes nil before assigning healthStatus.

Files Needing Attention: pages/plural-features/continuous-deployment/deployment-operator/custom-health.md

_{Reviews (1): Last reviewed commit: "docs: add CustomHealth Lua authoring gui..." | Re-trigger Greptile}

A few improvments:

1. The example customhealthobject should be:

apiVersion: deployments.plural.sh/v1alpha1
kind: CustomHealth
metadata:
  name: example-ready-condition
  namespace: <namespace>
spec:
  group: example.io
  version: v1
  kind: Example
  script: |
    healthStatus = { status = "Unknown" }

    if Obj.status ~= nil and statusConditionExists(Obj.status, "Ready") then
      healthStatus = { status = "Progressing" }
      if isStatusConditionTrue(Obj.status, "Ready") then
        healthStatus = { status = "Healthy" }
      end
    end

2. The correct built-in functions are referenced there statusConditionExists isStatusConditionTrue, etc. We should document each explicitly.
3. We should document the expected status values, again based on this
4. We should explain this is a deployment-operator api, so needs to be placed on each cluster it should be applied to, ideally via a global service.