Initialize WebAuthn registration

curl --request POST \
  --url https://{tenant_id}.hanko.io/webauthn/registration/initialize

{
  "publicKey": {
    "rp": {
      "name": "Hanko Authentication Service",
      "id": "localhost"
    },
    "user": {
      "id": "pPQT9rwJRD7gVncsnCDNyN",
      "name": "user@example.com",
      "displayName": "user@example.com"
    },
    "challenge": "7qmkJUXR0dOFnsW48evX3qKdCzlGjvvqAAvMDN+KTN0=",
    "pubKeyCredParams": [
      {
        "type": "public-key",
        "alg": -7
      }
    ],
    "timeout": 60000,
    "authenticatorSelection": {
      "authenticatorAttachment": "platform",
      "requireResidentKey": true,
      "residentKey": "preferred",
      "userVerification": "required"
    },
    "attestation": "none"
  }
}