gitops: observability stack (Loki/Promtail/Grafana), Grafana Ingress, Argo multi-source

- Add gitops/observability umbrella chart with vendored Helm deps
- Grafana Ingress: Traefik, letsencrypt-prod, grafana.k8s.selair.it + root_url
- Argo Application: spec.sources (onelab + onelab-obs)
- OneLab: configuration secret override, compliance/LDAP values, logs.path /logs
- Docs: OBSERVABILITY, BOOTSTRAP, README, instance-overrides example

Made-with: Cursor

gitops/observability/Chart.yaml

@@ -0,0 +1,16 @@
+apiVersion: v2
+name: onelab-observability
+description: Loki + Promtail + Grafana for OneLab (same Argo Application as app chart via multi-source).
+type: application
+version: 0.1.0
+appVersion: "1.0"
+dependencies:
+  - name: loki
+    version: 6.55.0
+    repository: https://grafana.github.io/helm-charts
+  - name: promtail
+    version: 6.17.1
+    repository: https://grafana.github.io/helm-charts
+  - name: grafana
+    version: 10.5.15
+    repository: https://grafana.github.io/helm-charts