added systemd service and installation file

agent/systemd/keywarden-agent.env.example

@@ -0,0 +1,13 @@
+# Keywarden server URL (required on first boot if /etc/keywarden/agent.json does not exist)
+KEYWARDEN_SERVER_URL=https://keywarden.example.com/api/v1
+
+# Enrollment token used only for first enrollment / forced re-enrollment.
+# Remove after successful enrollment.
+KEYWARDEN_ENROLL_TOKEN=
+
+# Optional path to a private CA PEM for verifying the Keywarden server TLS cert.
+# KEYWARDEN_SERVER_CA_PATH=/etc/ssl/certs/keywarden-ca.pem
+
+# Optional override for the persisted per-agent token in agent.json.
+# Normally leave unset.
+# KEYWARDEN_AGENT_API_TOKEN=