feat: major restructuring in migration to terragrunt

- migrate from individual terraform files to config-driven terragrunt module structure
- add vault_cluster module with config discovery system
- replace individual .tf files with centralized config.hcl
- restructure auth and secret backends as configurable modules
- move auth roles and secret backends to yaml-based configuration
- convert policies from .hcl to .yaml format, add rules/auth definition
- add pre-commit hooks for yaml formatting and file cleanup
- add terragrunt cache to gitignore
- update makefile with terragrunt commands and format target

policies/auth/k8s/au/syd1/admin.yaml

@@ -0,0 +1,23 @@
+# Allow administration of Kubernetes authentication backend
+---
+rules:
+  - path: "auth/k8s/au/syd1/config"
+    capabilities:
+      - create
+      - update
+      - read
+      - delete
+  - path: "auth/k8s/au/syd1/role/*"
+    capabilities:
+      - create
+      - update
+      - read
+      - delete
+      - list
+  - path: "auth/k8s/au/syd1/role"
+    capabilities:
+      - list
+
+auth:
+  approle:
+    - tf_vault