Closes #514.

CI: test building freedesktop-sdk overnight

Closes #514

See merge request !826

The current one doesn't build due server being down.

To finish the creation of the Let's Encrypt certificate, which will
allows us to use https://docs.buildstream.build/ for accessing the
documentation.

ci: add ACME challenge

See merge request !831

Imports code.proto from https://github.com/googleapis/googleapis and
corresponding modules generated with ./setup.py build_grpc.

#668

#668