[MOPU-288] Add related links to monitor templates

[vuvkar]

Summary

• Add ## Related Links sections to kubernetes, postgres, and redis monitor templates (these were entirely missing)
• Append specific metric/log/infrastructure links to existing nginx monitor templates (4xx, 5xx, upstream_peer_fails)
• All links are scoped with template variables (e.g., {{kube_cluster_name.name}}) for quick access to relevant data during incidents

Integrations updated: kubernetes (8 monitors), nginx (3 monitors), postgres (2 monitors), redis (1 monitor)

Test plan

• All 14 edited JSON files validated with python3 -c "import json; json.load(open(...))" — no parse errors
• Review that added links match the metrics/tags used in each monitor query

🤖 Generated with Claude Code

[github-actions]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.