Packaging: the binary and package are inbuxa, INBUXA_* settings with STALWART_* fallback

- crates/main: package and [[bin]] renamed to inbuxa; homepage inbuxa.org;
  license AGPL-3.0-only (upstream is dual; the fork takes the AGPL).
- types::branding::env_var reads INBUXA_<name>, falling back to
  STALWART_<name> with a warning, for all nine server settings.
  STALWART_APP_ and STALWART_SPAM_* storage keys are unchanged.
- New-install default paths /var/lib/inbuxa and /var/log/inbuxa.
- Dockerfiles, systemd unit, launchd plist and AppArmor profile renamed.
- Upstream's .github moved to .github-upstream so none of it runs.
- install.sh stubbed: upstream's would install Stalwart.
- Two missed brand strings: the SMTP Received header and the utils user agent.

crates/smtp/src/inbound/data.rs

@@ -1051,7 +1051,7 @@ impl<T: SessionStream> Session<T> {
         }
         headers.extend_from_slice(b"by ");
         headers.extend_from_slice(self.hostname.as_bytes());
-        headers.extend_from_slice(b" (Stalwart SMTP) with ");
+        headers.extend_from_slice(concat!(" (", types::brand!(), " SMTP) with ").as_bytes());
         headers.extend_from_slice(match (self.stream.is_tls(), !self.is_authenticated()) {
             (true, true) => b"ESMTPS",
             (true, false) => b"ESMTPSA",