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/common/src/manager/defaults.rs

@@ -529,7 +529,7 @@ async fn insert_safe_defaults(bp: &mut Bootstrap) -> trc::Result<()> {
                     ansi: false,
                     prefix: "stalwart.log".into(),
                     rotate: LogRotateFrequency::Daily,
-                    path: "/var/log/stalwart".into(),
+                    path: "/var/log/inbuxa".into(),
                     ..Default::default()
                 })
                 .into(),