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/kv/service/repoflow/au/syd1/ceph-s3/read.hcl

@@ -1,3 +0,0 @@
-path "kv/data/service/repoflow/au/syd1/ceph-s3" {
-  capabilities = ["read"]
-}

policies/kv/service/repoflow/au/syd1/ceph-s3/read.yaml

@@ -0,0 +1,10 @@
+# Allow reading Repoflow Ceph S3 configuration
+---
+rules:
+  - path: "kv/data/service/repoflow/au/syd1/ceph-s3"
+    capabilities:
+      - read
+
+auth:
+  k8s/au/syd1:
+    - repoflow