This reverts commit 620c9332 (stack/erp5: stop using caucase managed
certificate for balancer, 2020-11-10) with an updated design. We add a
caucase service for balancer in the balancer partition. The caucase
service from the root partition (that was not used) is removed.

The underlying idea is that the default configuration should use multiple
caucases with limited scope, here we have one caucase to manage the
certificate used by haproxy server in the balancer partition, so we put
one caucase to manage this certificate and the caucase is configured to
auto-accept one certificate only. The plan is that when we will add a
certificate for mariadb server, we'll add another caucase inside this
mariadb server.

For more advanced usage and also to support the cases where a new
certificate needs to be re-emitted for some reason, users can request
with an existing caucase URL. In that case, they will have to accept
the certificate requests.

Notable changes:

balancer/ssl/caucase-url is no longer documented in parameters, this is
an internal parameter, users can pass one global caucase service to
manage all partition

CAUCASE environment variable is no longer set when running zope. There
was no identified use case and with this new approach of multiple
caucases, the term "caucase" alone became ambiguous.