`cockroach connect join` gets confused by CA key file format

[knz]

I was trying to do QA for #63492 and ran into the following error:

ERROR: failed to initialize host certs after writing CAs to disk: 
  failed to load or create InterNode certificates: 
  failed to create Service Cert and Key: 
  failed to parse valid Private Key from PEM blob: 
  x509: failed to parse private key (use ParsePKCS8PrivateKey instead for this key format)

This is because this particular ca.key on the existing node is stored indeed as a PKCS#8 package, not PKCS#1. I found out in Go's own tls package that the CA key is customarily loaded like this:

  if key, err := x509.ParsePKCS1PrivateKey(der); err == nil {
    return key, nil
  }
  if key, err := x509.ParsePKCS8PrivateKey(der); err == nil {
    switch key := key.(type) {
    case *rsa.PrivateKey, *ecdsa.PrivateKey, ed25519.PrivateKey:
      return key, nil
    default:
      return nil, errors.New("tls: found unknown private key type in PKCS#8 wrapping")
    }
  }
  if key, err := x509.ParseECPrivateKey(der); err == nil {
    return key, nil
  }

  return nil, errors.New("tls: failed to parse private key")

Which is why we hadn't noticed this problem before.

Jira issue: CRDB-7356
Epic: CRDB-6663