public static HttpAsyncClientBuilder create() {
        return create(
                tlsStrategy -> PoolingAsyncClientConnectionManagerBuilder.create()
                        .setTlsStrategy(tlsStrategy)
                        .build());
    }
Async http client builder for internal Vespa communications over http/https.
Configures Vespa mTLS and handles TLS mixed mode automatically.
Client should only be used for requests to Vespa services.

Caveats:
- custom connection manager must be configured through {@link #create(AsyncConnectionManagerFactory)}.

@author bjorncs
http-utils/src/main/java/ai/vespa/util/http/hc5/VespaAsyncHttpClientBuilder.java