This commit enables FTS via Xapian, and exposes the port required for
ManagedSieve integration with Dovecot; additionally, bugs in the
integration of LMTP with RSpamd have been fixed.
In support of these changes, configuration files that were previously
split into container-based and service-based are now consolidated, and
we now ensure that only our own container-based configuration is used
when running Dovecot.
This includes setting the Debian base image to a specific release rather
than the generic `stable` version, which can cause issues when assuming
package versions or external repository status.
This contains the culmination of work done privately for a few months,
and is intended to be a solid basis for other peoples' experimentations
with setting up single-node, home-server setups using Fedora CoreOS.
