1. go-smtp is replaced by a fork that reverts StartTLS removal.
2. SASL LOGIN is no longer supported by upstream go-sasl, readded disabled by default.
3. Updated endpoint code to match new go-smtp authentication interfaces.
4. certmagic repo had some renames
5. Minimum Go version increased to 1.23 to match dependencies.
1. Clarify that you need to manually create the user and group
when building from source. ./build.sh does not do that since
it is a packaging tool, not system configuration one.
2. Do not require "go" command to be present when running
./build.sh install. go installation may be user-specific and
unavailable when running with sudo.
3. Ease UMask restrictions. Allow group access.
This allows CLI commands to be run by any user in maddy group.
See #569.
