Update env.j2 to support the new configuration

roles/custom/matrix-element-call/templates/env.j2

@@ -1,9 +1,10 @@
 # Environment variables for Element Call
 ELEMENT_CALL_SERVER_URL=https://{{ matrix_element_call_domain }}
 LIVEKIT_SERVICE_URL={{ matrix_element_call_livekit_service_url }}
+LIVEKIT_SECRET={{ matrix_element_call_livekit_dev_key }}
 JWT_SERVICE_URL={{ matrix_element_call_jwt_service_url }}
 
 # Optional additional environment variables provided by the user
 {% for key, value in matrix_element_call_environment_variables_additional.items() %}
 {{ key }}={{ value }}
-{% endfor %}
+{% endfor %}