@Nullable
    default Boolean tlsAllowUnsafeCiphers() {
        return null;
    }
Returns whether to allow the bad cipher suites listed in
<a href="https://datatracker.ietf.org/doc/html/rfc7540#appendix-A">RFC7540</a> for TLS handshake.
Note that this flag has no effect if a user specified the value explicitly via
{@link ClientFactoryBuilder#tlsAllowUnsafeCiphers(boolean)}.

<p>This flag is disabled by default. Specify the
{@code -Dcom.linecorp.armeria.tlsAllowUnsafeCiphers=true} JVM option to enable it.
core/src/main/java/com/linecorp/armeria/common/FlagsProvider.java