feat: add GCP Terraform deployment support

driver-redpanda/deploy/gcp/README.md

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+# Redpanda Benchmark — GCP Deployment
+
+Deploy Redpanda brokers and OMB benchmark clients on GCP using Terraform + Ansible.
+
+## Prerequisites
+
+1. [Terraform](https://developer.hashicorp.com/terraform/install) >= 1.0
+2. [gcloud CLI](https://cloud.google.com/sdk/docs/install) authenticated:
+   ```bash
+   gcloud auth application-default login
+   ```
+3. Compute API enabled in your project:
+   ```bash
+   gcloud services enable compute.googleapis.com --project=<your-project>
+   ```
+4. An SSH key pair:
+   ```bash
+   ssh-keygen -t rsa -f ~/.ssh/redpanda_gcp
+   ```
+
+## Usage
+
+```bash
+cd driver-redpanda/deploy/gcp
+
+cp terraform.tfvars.example terraform.tfvars
+# Edit terraform.tfvars — set project_name, ssh_user, public_key_path at minimum
+
+terraform init
+terraform apply
+```
+
+Run Ansible from the `deploy/` directory (one level up — `hosts.ini` is written there by Terraform).
+`ansible.cfg` hardcodes `~/.ssh/redpanda_aws`, so pass your GCP key explicitly with `--private-key`.
+
+**Standalone Redpanda cluster:**
+```bash
+cd ..
+ansible-playbook deploy.yaml -i hosts.ini --private-key ~/.ssh/redpanda_gcp
+```
+
+**Against an existing BYOC/Dedicated cluster** (set `num_instances.redpanda = 0` in tfvars):
+```bash
+cd ..
+ansible-playbook deploy.yaml -i hosts.ini \
+  --private-key ~/.ssh/redpanda_gcp \
+  --ask-become-pass \
+  -e "tls_enabled=true sasl_enabled=true sasl_username=<user> sasl_password=<password>" \
+  -e "bootstrapServers=<seed-host>:9092"
+```
+
+> `--ask-become-pass` is needed when running Ansible from a local Mac (the playbook has tasks requiring sudo). Omit it when running from a cloud VM as root.
+
+## VPC Peering (optional)
+
+Set `byoc_vpc_name` in `terraform.tfvars` to peer the benchmark network with an existing
+BYOC network. `terraform apply` creates peering in both directions automatically.
+
+### IAM requirement
+
+Your credentials need `compute.networks.addPeering` on both the benchmark project and the
+BYOC project. Grant it with:
+
+```bash
+gcloud projects add-iam-policy-binding <byoc-project> \
+  --member="user:<your-email>" \
+  --role="roles/compute.networkAdmin"
+```
+
+### Fallback: manual peering
+
+If you cannot obtain IAM access to the BYOC project (e.g. it is managed by Redpanda),
+create the return peering manually after `terraform apply`:
+
+```bash
+BENCHMARK_NETWORK=$(terraform output -raw benchmark_network_name)
+BENCHMARK_PROJECT=<your-benchmark-project>
+
+gcloud compute networks peerings create rp-byoc-to-benchmark \
+  --network=<your-byoc-network> \
+  --peer-project=$BENCHMARK_PROJECT \
+  --peer-network=$BENCHMARK_NETWORK \
+  --project=<byoc-project>
+```