The previous instructions for disabling the default site left things in
an in-between state: it still returned an error page and did not disable
the default HTTPS site unless the user figured out how to generate
a valid SSL certificate.
The changes made in this commit assume that the user actively disabling
the default site considers all requests to unknown vhosts as bogus.
Therefore there is no point in responding and providing a valid SSL
certificate to them.
As such, the recommended error code is now `444` to close the connection
without responding and the HTTPS default site is disabled with
a self-signed certificate.
Also as all distributions supported by Dokku use systemd, make use of it
instead of the legacy `service` command which does not work anymore on
some distributions like Arch.
The previous method was a bit more difficult for users to interact with as they needed to ensure the file was at a certain path in the built image. This change divorces the file from the built artifact, better aligning the nginx.conf.sigil handling with the rest of Dokku's monorepo support.
A side effect of this is now building proxy configurations does not require access to the built image.
Closes#5207
