fix: Properly handle metrics aggregation with room data

[juliusknorr]

• Join a room
• Requets the metrics endpoint

Before

TypeError: Cannot convert undefined or null to object
    at Function.keys (<anonymous>)
    at file:///app/websocket_server/SystemMonitor.js:36:78
    at Array.reduce (<anonymous>)
    at SystemMonitor.getRoomStats (file:///app/websocket_server/SystemMonitor.js:36:43)
    at SystemMonitor.getSystemOverview (file:///app/websocket_server/SystemMonitor.js:16:20)
    at PrometheusDataManager.updateMetrics (file:///app/websocket_server/PrometheusDataManager.js:37:39)
    at AppManager.metricsHandler (file:///app/websocket_server/AppManager.js:36:23)
    at Layer.handleRequest (/app/node_modules/router/lib/layer.js:145:17)
    at next (/app/node_modules/router/lib/route.js:159:13)
    at Route.dispatch (/app/node_modules/router/lib/route.js:119:3)

After

No more error

Follow up

• Cleanup storage manager to properly prefix rooms as now also other data is stored (token/socket data)