Migrating the website

[Sander Striker <s....@striker.nl>]

Hi,

We still want to migrate the website over and now is as good a time as
any.  I created the https://github.com/apache/buildstream-site repository
for a start.  Basically the first step in
https://infra.apache.org/asf-pelican-gettingstarted.html.

Once we have it in place https://buildstream.apache.org can stop
redirecting to https://petri.apache.org/buildstream.  We also should look
into redirecting https://buildstream.build/ to
https://buildstream.apache.org.

I'm happy to help drive, but certainly won't be offended if someone beats
me to it.

Cheers,

Sander