test: add e2e tests for certificate revocation (#1345)

## Summary

- Add end-to-end tests for certificate revocation functionality
- Test that a revoked client certificate cannot connect to the VPN
- Test that a new certificate can be created with the same name as a
revoked one (validating the fix from #1185)
- Test that the new certificate can successfully connect

## Test Flow

1. **Initial connectivity tests** - existing tests pass
2. **Certificate revocation test**:
   - Create a new client `revoketest`
   - Connect with the certificate (verifies it works)
   - Disconnect the client
   - Revoke the certificate via the install script
- Try to reconnect with revoked cert (verifies connection is rejected)
3. **Reuse revoked name test**:
   - Create a new certificate with the same name `revoketest`
   - Verify both revoked and valid entries exist in `index.txt`
   - Connect with the new certificate (verifies it works)

## Changes

| File | Changes |
|------|---------|
| `test/server-entrypoint.sh` | Start OpenVPN in background, add
revocation test orchestration |
| `test/client-entrypoint.sh` | Add revocation test phases with signal
file coordination |
| `docker-compose.yml` | Remove read-only restriction on shared volume
for client |
| `Makefile` | Increase timeout from 60 to 180 iterations |
| `.github/workflows/docker-test.yml` | Increase timeouts, fix shared
volume |

docker-compose.yml

@@ -36,7 +36,7 @@ services:
     devices:
       - /dev/net/tun:/dev/net/tun
     volumes:
-      - shared-config:/shared:ro
+      - shared-config:/shared
     networks:
       vpn-test:
         ipv4_address: 172.28.0.20