Be able to configure a different archive server URL for the rest api

[cindyzczhao]

Is your feature request related to a problem? Please describe.
Currently, the archive host URL in the rest api is forced to include the archive server port.
The user should be able to configure this to hit a different external URL if desired.

Describe the solution you'd like
An additional argument in the atlas-server start command to specify the other URL.

[mohammedri]

How does this work currently with an instance of Atlas that is in a remote machine? The external URL needs to be configured to be able to access the artifact from that remote server no?

[cindyzczhao]

Currently we assume the {archive host}:{archive port} is the external URL for getting artifacts. But if that's not the case, there's no way for the user to change it.

[shazraz]

Our current setup doesn't put the archive server behind the auth proxy, as a result things break when setting things behind an internet facing proxy.