Add secrets module: Spring Cloud Vault, AWS Secrets Manager, Kubernetes configtree and Jasypt on Spring Boot 4.1.2, with real transcripts

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b6tTs7ivgTNq4ZrurU

secrets/k8s/deployment-snippet.yaml

@@ -0,0 +1,18 @@
+# Pod spec fragment wiring the Secret above into Spring Boot. NOT applied to a cluster in this
+# module: the config tree layout it relies on is reproduced in KubernetesConfigtreeTest.
+spec:
+  containers:
+    - name: app
+      image: example/secrets-demo:1.0.0
+      env:
+        - name: SPRING_CONFIG_IMPORT
+          value: "configtree:/etc/secrets/db/"
+      volumeMounts:
+        - name: db-credentials
+          mountPath: /etc/secrets/db
+          readOnly: true
+  volumes:
+    - name: db-credentials
+      secret:
+        secretName: db-credentials
+        defaultMode: 0400