feat(server): log scan request received before vulnerability detection

[Hritik914]

Log an informational message in VulsHandler.ServeHTTP when a scan request is received, prior to starting package vulnerability detection and CVE data enrichment.

[Hritik914]

Hi @MaineK00n
Our vuls instance is running in server mode and some of our servers give 1200+ packages for scan and it oom kills the pod with 2Gi memory. we have increased it to 6Gi but the memory usage keeps increasing. mean while the request from our server is timeout out as it is set to 15 mins ( have tested it with 100 mins, but it gets timedout).

So having a request received log would be immensely helping in debugging as well as for any metrics we might want to expose.

This is my first PR in open source. Please guide me if i had missed something.

Thanks