`polling_url` should be externally reachable

[lukpueh]

#47 added the dependencytrack polling url to a successful upload response. The host part of the url is sourced from config:

pia/pia/main.py

Line 225 in c5b263b

dt_url = str(settings.dependency_track_url).rstrip("/")

In our deployment this url is no reachable externally, and thus not useful to the caller.

Options are:

• configure and use externally reachable url, or (more effort for us)
• only display path or token (more effort for the user)