Enable UserParameterDir on Windows agent config

The Windows agent config template was missing the active
UserParameterDir=${ZBX_USERPARAMETERDIR} line. The Windows agent Dockerfile
sets ZBX_USERPARAMETERDIR and creates the C:\zabbix\user_scripts directory,
but because the option is never written to the config, user parameter scripts
placed there are not loaded by the agent.

The Linux agent, Linux agent2, and Windows agent2 templates all set this
option; only the Windows agent template was missing it. Add it to match.

templates/config/agent_windows/zabbix_agentd_user_parameters.conf

@@ -33,3 +33,5 @@ UnsafeUserParameters=${ZBX_UNSAFEUSERPARAMETERS}
 # Mandatory: no
 # Default:
 # UserParameterDir=
+
+UserParameterDir=${ZBX_USERPARAMETERDIR}