GitlabApi does not use proxy for Oauth2 Token requests

[suved-mahajan]

GitlabApi class Oauth2 login methods do not use proxy to acquire oauth2 token, for this reason I am facing ConnectException : Connection Refused to the server. Line : https://github.com/gitlab4j/gitlab4j-api/blob/37617ec31bd2888f421c8bd5586727e40c51ba09/src/main/java/org/gitlab4j/api/GitLabApi.java#L279 can be changed to use proxy configuration : GitLabApi gitLabApi = new GitLabApi(apiVersion, url, (String)null, (String) null, clientConfigProperties);

Attached a file that demonstrates the usage of proxy GitLabApi_WithProxy.zip .