Add ability to pass in HttpClient into ArtifactoryClient factory method(s)

[btiernay]

This is to avoid single connection issues in concurrent environments:

java.lang.IllegalStateException: Invalid use of BasicClientConnManager: connection still allocated.

by using a pooling connection manager implementation, as an example.

[bhuvneshj]

Hey, I ran into the same issue, did you figure out a workaround to upload files in parallel? Stuck on this issue since past 2 days, ironically a relief that I am not alone. Thought I could use your experience on this. Any tips?

[eyalbe4]

@btiernay and @bhuvneshj, Thanks for sharing this need. We will soon start working on implementing this.