Secruity Scan for Docker Image and fix for Issue #6

[jerusdp]

Changes

• Fix for issue Main.yml GitHub action tests current version of lambda-rust #6
• Test job in main.yml GitHub action now builds the new image and tests against the new image
• Scan job added to main.yml to provide a security scan of the built image and verify no HIGH or CRITICAL vulnerabilities (that have fixes)
• Build generates tests based on the name of the repository (to facilitate testing in other repository)
• Publication only runs when the repository is rust-serverless/lambda-rust and depends on successful Scan and Test jobs
• Dockerfile fixes to run yum update and remove the original kernel-devel package