Support more GO module providers such as the use of BitBucket and custom URLs

Feature description: 
When creating a remote GO repository, Artifactory is able to fetch modules from Github and Artifactory only.
Artifactory should be able also to fetch modules from none Github or Artifactory repositories by giving the ability to use custom URLs and vanity URLs such as Bitbucket or Gitlab in order to access different private GO repositories.

What is the expected behavior? 

This way we can utilize a remote Go repository in Artifactory serves as a caching proxy to Bitbucket or GitLab.