add initial malware scan support

[janjwerner-confluent]

This PR introduces the malware scan for librdkafka. Scan results are stored in s3 for unix / macos builds and in Semaphore artifact storage for Windows builds.

[janjwerner-confluent]

@emasab Can you please look at the build failures related to package downloads. I believe that the failures are not related to the addition of the malware scans.