migrate to Buildhub2

[willkg]

pushlog-addon is using Buildhub:

https://github.com/mozilla/pushlog-addon/blob/master/content.js#L121

Buildhub is deprecated and will be decommissioned in July. See mozilla-services/buildhub#532 for details.

There are API docs here:

https://buildhub2.readthedocs.io/en/latest/user.html

This issue covers migrating pushlog-addon to Buildhub2.

[willkg]

I talked with @calixteman about this and it's probably something we should absorb into Socorro. I wrote up a bug to look into that, but it's probably not something I can do any time soon.

https://bugzilla.mozilla.org/show_bug.cgi?id=1562247