MEDIUM: acme: replace the previous ckch instance with new ones

MEDIUM: acme: replace the previous ckch instance with new ones

This step is the latest to have a usable ACME certificate in haproxy.

It looks for the previous certificate, locks the "BIG CERTIFICATE LOCK",
copy every instance, deploys new ones, remove the previous one.
This is done in one step in a function which does not yield, so it could
be problematic if you have thousands of instances to handle.

It still lacks the rate limit which is mandatory to be used in
production, and more cleanup and deinit.