default ArtifactoryClient http.Transport missing some useful defaults

[jbardin]

NewClient uses a mostly empty http.Transport, which is missing some useful defaults for timeouts, proxy, etc.

Good starting values are usually what's provided by http.DefaultTransport, something like:

var defaultTransport = &http.Transport{
        Proxy: http.ProxyFromEnvironment,
        DialContext: (&net.Dialer{
                Timeout:   30 * time.Second,
                KeepAlive: 30 * time.Second,
                DualStack: true,
        }).DialContext,
        MaxIdleConns:          100,
        IdleConnTimeout:       90 * time.Second,
        TLSHandshakeTimeout:   10 * time.Second,
        ExpectContinueTimeout: 1 * time.Second,
}

[lusis]

Good call. I'll pull those in! Thanks!

[xocasdashdash]

@lusis Any idea when do you think you can implement this? I can get a PR done if it helps!