Allow customers to specificy underlying semgrep commandline args
Problem
In some circumstances, customers may want to provide underlying commandline args directly to semgrep. Right now we disallow this as it would potentially increase burden on supporting unknown commandlines. However, sometimes a customer may need to provide a flag we don't support to get the analyzer to even work in their environment.
Solution
Allow customers to pass in arguments directly to semgrep but also require an --unsupported
boolean flag to alert that we can NOT support this configuration/pipeline if something goes wrong. Also we should print out a warning banner.