When I try to start Dovecot, it will complain if `/var/run/maddy/` is missing as it can't create /var/run/maddy/dovecot-lmtp.sock`.
When I try to start Maddy, it complains that `unix:///var/run/dovecot/auth-maddy-client` doesn't exist.
Therefore I can't start either service.
I decided to move the LMTP socket into Dovecot's runtime directory since it provides the socket,
and to remove the sock extension to match the naming convention in the rest of the directory.
Security for LMTP should be configured using Implicit TLS that is
already supported using tls:// scheme for addresses. TLS
is also unnecessary for most LMTP use-cases (Unix sockets, etc) and
attempting STARTTLS caused issues in the past (see #309).
