Use downloads.a.o instead of archive

Hello, Apache PMCs,

In order to better provide our millions of users with downloads, the
Apache Infrastructure Team has been restructuring the way downloads work
for our main distribution channels in the past few weeks. For users,
this will largely go unnoticed, and for projects likely the same, but we
did want to reach out to projects and inform them of the changes we've
made:

As of March 2020, we are deprecating www.apache.org/dist/ in favor of
https://downloads.apache.org/ for backup downloads as well as signature
and checksum verification. The primary driver has been splitting up web
site visits and downloads to gain better control and offer a better
service for both downloads and web site visits.

As stated, this does not impact end-users, and should have a minimal
impact on projects, as our download selectors as well as visits to
www.apache.org/dist/ have been adjusted to make use of
downloads.apache.org instead. We do however ask that projects, in their
own time-frame, change references on their own web sites from
www.apache.org/dist/ to downloads.apache.org wherever such references
may exist, to complete the switch in full. We will NOT be turning off
www.apache.org/dist/ in the near future, but would greatly appreciate if
projects could help us transition away from the old URLs in their
documentation and on their download pages.

The standard way of uploading releases[1] will STILL apply, however
there may be a short delay (<= 15 minutes) between releasing and
releases showing up on downloads.apache.org for technical reasons.

If you have any questions about this change, please do not hesitate
to reach out to us at users@infra.apache.org.

With regards,
Daniel on behalf of ASF Infrastructure.