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/utils/src/http.rs

@@ -145,7 +145,7 @@ pub fn build_http_client(
     allow_invalid_certs: bool,
 ) -> Result<Client, String> {
     let mut headers = build_http_headers(raw_headers, username, password, token, content_type)?;
-    headers.insert(USER_AGENT, "Stalwart/1.0.0".parse().unwrap());
+    headers.insert(USER_AGENT, "INBUXA/1.0.0".parse().unwrap()); // types::brand!(); utils does not depend on types
 
     match http_client_builder(allow_invalid_certs)
         .connect_timeout(timeout)