Generalized security scan

[mlholland]

Takes code from the following files:

• https://github.com/solo-io/gloo/blob/master/docs/cmd/securityscanutils/securityscan_utils.go
• https://github.com/solo-io/gloo/blob/master/docs/cmd/generate_docs.go

... And merges them into a single CLI that has a bunch of extra inputs to make it completely repo-agnostic. BOT NOTES: resolves https://github.com/solo-io/go-utils/issues/467

[solo-changelog-bot[bot]]

Issues linked to changelog: https://github.com/solo-io/go-utils/issues/467