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/registry/src/schema/structs_impl.rs

@@ -4143,7 +4143,7 @@ impl Default for Bootstrap {
             request_tls_certificate: true,
             generate_dkim_keys: true,
             data_store: DataStore::RocksDb(RocksDbStore {
-                path: "/var/lib/stalwart/".to_string(),
+                path: "/var/lib/inbuxa/".to_string(),
                 ..Default::default()
             }),
             blob_store: BlobStore::Default,
@@ -4151,7 +4151,7 @@ impl Default for Bootstrap {
             in_memory_store: InMemoryStore::Default,
             directory: DirectoryBootstrap::Internal,
             tracer: Tracer::Log(TracerLog {
-                path: "/var/log/stalwart/".to_string(),
+                path: "/var/log/inbuxa/".to_string(),
                 ..Default::default()
             }),
             dns_server: DnsServerBootstrap::Manual,