Hybrid RSA and ECC setup

Is it possible to generate a certificate with an RSA key and one with an ECC key to serve both in a hybrid configuration using lua-resty-autossl? Same as the following nginx configuration:
```
server {
listen 443 ssl;
# RSA certificate
ssl_certificate /etc/certificates/fullchain.rsa.pem;
ssl_certificate_key /etc/certificates/privkey.rsa.pem;

# ECDSA certificate
ssl_certificate /etc/certificates/fullchain.ecc.pem;
ssl_certificate_key /etc/certificates/privkey.ecc.pem;
...
}
```

TLS handshakes are faster for ECC certificates and use less CPU resources, but because they are only supported by modern browsers a RSA fallback is still required.

Compare the requested nginx server configuration with lua-resty-autossl's existing certificate-generation and configuration behavior. Determine whether serving both RSA and ECC certificates is supported, and identify the configuration or implementation changes needed if it is not; completion should include a documented, tested path or a clear limitation.

Written by the indexing model from the issue text.