Upgrade Thanos chart 15.9.2

[anders-elastisys]

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What does this PR do / why do we need this PR?

Upgrades Thanos chart to 15.9.2 and Thanos image to v0.37 to keep it up to date.
Also refactored the Helmfile values files for Thanos to have a common values file to disable all Thanos components, and let each component be enabled in the separate values files used per release.
Also removes alertmanager image override (see this PR for context).
New Thanos bitnami image for v0.37 has been pushed to Elastisys GitHub registry mirror. Due to new image validation added to all bitnami charts, needed to set global.security.allowInsecureImages=true.

• Fixes Upgrade thanos #1600

Information to reviewers

Checklist

• Proper commit message prefix on all commits
• Change checks:
  • The change is transparent
  • The change is disruptive
  • The change requires no migration steps
  • The change requires migration steps
  • The change updates CRDs
  • The change updates the config and the schema
• Documentation checks:
  • The public documentation required no updates
  • The public documentation required an update - [link to change](set-me)
• Metrics checks:
  • The metrics are still exposed and present in Grafana after the change
  • The metrics names didn't change (Grafana dashboards and Prometheus alerts required no updates)
  • The metrics names did change (Grafana dashboards and Prometheus alerts required an update)
• Logs checks:
  • The logs do not show any errors after the change
• PodSecurityPolicy checks:
  • Any changed Pod is covered by Kubernetes Pod Security Standards
  • Any changed Pod is covered by Gatekeeper Pod Security Policies
  • The change does not cause any Pods to be blocked by Pod Security Standards or Policies
• NetworkPolicy checks:
  • Any changed Pod is covered by Network Policies
  • The change does not cause any dropped packets in the NetworkPolicy Dashboard
• Audit checks:
  • The change does not cause any unnecessary Kubernetes audit events
  • The change requires changes to Kubernetes audit policy
• Falco checks:
  • The change does not cause any alerts to be generated by Falco
• Bug checks:
  • The bug fix is covered by regression tests