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/pki_secret_backend_role/pki/au/syd1/servers_default.yaml

@@ -0,0 +1,17 @@
+backend: "pki/au/syd1"
+allow_ip_sans: true
+allowed_domains:
+  - "unkin.net"
+  - "*.unkin.net"
+  - "localhost"
+allow_subdomains: true
+allow_glob_domains: true
+allow_bare_domains: true
+enforce_hostnames: true
+allow_any_name: true
+max_ttl: 7776000  # 2160 * 3600
+key_bits: 4096
+country:
+  - "Australia"
+use_csr_common_name: true
+use_csr_sans: true