public static String defaultBackoffSpec() {
        return DEFAULT_BACKOFF_SPEC;
    }
Returns the {@linkplain Backoff#of(String) Backoff specification string} of the default {@link Backoff}
returned by {@link Backoff#ofDefault()}. Note that this flag has no effect if a user specified the
{@link Backoff} explicitly.

<p>The default value of this flag is {@value DefaultFlagsProvider#DEFAULT_BACKOFF_SPEC}. Specify the
{@code -Dcom.linecorp.armeria.defaultBackoffSpec=<spec>} JVM option to override the default value.
core/src/main/java/com/linecorp/armeria/common/Flags.java