Import upstream v0.16.22, stripped

Upstream commit: 474dd0229cb20cf513036619781ed97bd8073c3f
Enterprise-only files removed or emptied: 63
Enterprise-only snippets removed: 117 in 50 files
Dangling module declarations removed: 5
Cargo edits turning enterprise off: 14
Verification: clean
Enterprise feature gates left for rebuilt features: 19 in 18 files

Produced by tools/fork/strip.py. The full report is in docs/fork/strip-reports/ on main.

resources/systemd/stalwart-mail.service

@@ -0,0 +1,21 @@
+[Unit]
+Description=Stalwart Server
+Conflicts=postfix.service sendmail.service exim4.service
+ConditionPathExists=__PATH__/etc/config.json
+After=network-online.target
+
+[Service]
+Type=simple
+LimitNOFILE=65536
+KillMode=process
+KillSignal=SIGINT
+Restart=on-failure
+RestartSec=5
+ExecStart=__PATH__/bin/stalwart --config=__PATH__/etc/config.json
+SyslogIdentifier=stalwart
+User=stalwart
+Group=stalwart
+AmbientCapabilities=CAP_NET_BIND_SERVICE
+
+[Install]
+WantedBy=multi-user.target