Wire most of nav v1 content into nav v2 (#3274)

Backports the YAML fill from demo/findability (PR #3268). Pure additions
to config/navigation-v2.yml within the existing structure — no schema
changes, no new directives. Closes most of the gap between v1 nav and
the nav-v2 prototype.

- Re-enable the commented Reference label and expand it: docs-content
  reference (top-level fanout), elasticsearch core/plugins/community-
  contributed, kibana, Cloud (cloud + cloud-on-k8s), Elasticsearch
  clients (java/js/dsl-js/.net/php/py/ruby/rs, eland, go-elasticsearch,
  curator), APM (k8s-attacher, aws-lambda, all agent libs), OpenTelemetry
  (opentelemetry root + motlp + edot-cloud-forwarder for AWS/Azure/GCP,
  edot-collector, all EDOT SDKs), ECS Logging (root + all per-language
  libs), beats, logstash, integration-docs, elasticsearch-hadoop,
  elastic-serverless-forwarder, ecs, search-ui, ecctl, plus
  aggregations/enrich-processor/query-languages/scripting-languages/
  text-analysis. ~1,200 pages.

- Wire children of 12 deploy-manage landings (security, users-roles,
  monitor, tools, remote-clusters, upgrade, cloud-organization,
  maintenance, api-keys, autoscaling, license, uninstall) under each
  existing `- group:` to preserve curated titles. ~370 pages.

- Convert distributed-architecture leaf entries into groups with
  canonical children: clusters-nodes-shards (node-roles),
  shard-allocation-relocation-recovery (shard-allocation-awareness +
  index-level-shard-allocation w/ delaying-allocation-when-node-leaves),
  discovery-cluster-formation (6 children).

- Convert production-guidance leaf entries into groups with their
  full canonical structure: Run Elasticsearch in production (Design
  for resilience [3 children], Scaling considerations, Performance
  optimizations [6 children]); Run Kibana in production (6 children).

- Convert ingest-reference-architectures leaf into a group with the
  16 canonical children grouped by architecture (Agent to Elasticsearch,
  Agent with Logstash, Agent with Kafka, Air-gapped, Logstash as input,
  Agent through a proxy). Set ingesting-data-for-elastic-solutions.md
  as the "Ingest by solution" group landing. Surface
  manage-data/ingest/tools.md alongside the existing API/upload entries.

- Add Release notes top-level label with the per-product release-notes
  tree (Elasticsearch + clients + Hadoop, Kibana, Elastic Agent,
  Fleet Server, Logstash, Beats, Serverless, Cloud Hosted, Cloud
  Enterprise, Cloud on K8s, Observability with EDOT SDKs and APM
  agents, Security, ECS, ECCTL).

- Add Troubleshoot top-level label as `- toc: docs-content://troubleshoot`
  (covers ~190 pages). Delete the dead Troubleshooting comment block
  whose entries are all already reachable via that toc.

- Replace 57 `{{templated}}` substitution tokens (in titles AND group
  labels) with their literal expansions per docs-content/docset.yml::
  features. The nav renderer does not expand `{{...}}` so leaving
  them caused literal `{{ece}}` etc. to render in the sidebar.

Skipped (depends on features added in later layers of the stack):
- Liam's Search and query rewrite (PR #3094, against this branch).
- Products section (introduced in hub-pages).
- island: entries (Logstash plugins/versioned plugins; needs
  nav-v2-sections).
- Observability page additions on demo (slot under groups added in
  hub-pages stack).

YAML valid. 173/173 navigation tests pass.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: theletterf