feat: add vault and consul roles for terraform-git (#73)

## Summary
- Add K8s auth role woodpecker_terraform_git for CI pipeline authentication
- Add consul secret backend role terraform-git for consul state storage tokens
- Add consul ACL policy granting write access to infra/terraform/git/ key prefix
- Add vault policy for reading consul creds at consul_root/au/syd1/creds/terraform-git

## Test plan
- [ ] Verify terragrunt plan succeeds
- [ ] Verify consul ACL policy is created correctly
- [ ] Verify K8s auth role can authenticate from woodpecker namespace

Reviewed-on: #73
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

policies/consul_root/au/syd1/creds/terraform-git.yaml

@@ -0,0 +1,9 @@
+---
+rules:
+  - path: "consul_root/au/syd1/creds/terraform-git"
+    capabilities:
+      - read
+
+auth:
+  k8s/au/syd1:
+    - woodpecker_terraform_git