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>

resources/secret_backend/consul_root/au/syd1/terraform-git.hcl

@@ -0,0 +1,7 @@
+key_prefix "infra/terraform/git/" {
+  policy = "write"
+}
+
+session_prefix "" {
+  policy = "write"
+}