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

config/auth_kubernetes_role/k8s/au/syd1/externaldns.yaml

@@ -0,0 +1,8 @@
+bound_service_account_names:
+  - externaldns
+bound_service_account_namespaces:
+  - externaldns
+token_ttl: 60
+token_policies:
+  - kv/service/kubernetes/au/syd1/externaldns/tsig/read
+audience: vault