public String hostnamePattern() {
        return hostnamePattern;
    }
Returns the hostname pattern of this virtual host, as defined in
<a href="https://datatracker.ietf.org/doc/html/rfc2818#section-3.1">the section 3.1 of RFC2818</a>.
core/src/main/java/com/linecorp/armeria/server/VirtualHost.java