As there is some kind of "collision" with request, allow to override
parameters.

Treat `<key>` as default and overwrite it with `frontend-config-<num>-<key>`,
instead of having the global `<key>` always passed to slaves.

This allows to request the partition with:

  monitor-httpd-frontend=12345
  -frontend-config-1-monitor-httpd-frontend=9876
  -frontend-config-1-monitor-httpd-frontend=8765

jinja2 template is required, as some paramters might come from the network.

jinja2 template is required, as some paramters might come from the network.

Removing 'secure' from cookie send by backend is plain wrong.

No custom_http nor custom_https shall publish information normally calculated.

It is used internally for communication between backend and the server.

Things are implemented elsewhere and tested, also some not-applicable.

mpm-watchdog promise is not applicable for Caddy.

Those kept are backward compatibility variables from the request.

Do not upper filenames nor users, use them as is.

bin/caddy-wrapper is not supported by signals sent to running caddy process.

As infromation passed to caddy-wrapper comes also from the network it
has to be templated using jinja2 in order to dump variables correctly.

By using 6tunnel workaround Caddy limitation of binding to only one
interface and in the result listen on IPv6.

Also drop needless "ipv6" keys across configuration.

If url is missing, the generated files shall be correct.

It requires a bit of changes into the template logic, as more
information has to be passed to each slave.

Dummy site is setup for Caddy to run.

This partially reverts commit 863507174c1c3c0365bfa35a7cf298a516b5946d.

Only instance part for nginx is kept, thus Caddy can start replace it.

%2F%2F is used to avoid double slashes cleanup with Caddy. See
https://github.com/mholt/caddy/issues/1298, which touches the problem,
but not enough for zope.