Add Scan API usage logs

[ray-roestenburg-da]

Add logs in Scan for every API call:

• the origin of the call (UI or active direct usage) by using a custom HTTP header when invoked from UI
• Add metrics (extract custom UI header in HttpServerMetrics, include 'from UI' flag in MetricsContext)
• "the API was called and source IP" are already logged in request logger

[moritzkiefer-da]

note that the request logger already includes the source ip and the api. so really the only thing that is missing is the origin