Fix resty client TLS client config setting error: current transport is not an *http.Transport instance

[magodo]

PR #58 is not correctly done, for the oauth2 clients, which are built when the security config is set to oauth2.

In the debug log, you'll notice error current transport is not an *http.Transport instance being raised from resty, which actually is from:

• https://github.com/go-resty/resty/blob/105f7185be505f070bfb19df4c3a4535058e0f84/client.go#L814-L816
• https://github.com/go-resty/resty/blob/105f7185be505f070bfb19df4c3a4535058e0f84/client.go#L1251-L1256

func (c *Client) Transport() (*http.Transport, error) {
	if transport, ok := c.httpClient.Transport.(*http.Transport); ok {
		return transport, nil
	}
	return nil, errors.New("current transport is not an *http.Transport instance")
}

The reason is that the oauth2 client's Transport field is not a *http.Transport, but *oauth2.Transport.

To fix this, when building the client, we initially create a default http client, which is of type http.Client, and move the tls config setting and the jar setting up right after this client is built. Then based on the security setting, we further create a resty.Client wrapping this default client, or wrapping an oauth2 client, which in turns wrapping this default client.