cli: Add --exclude-from-templates option to scanner scan command

The --exclude-from-templates helps in defining exclusion patterns by project type with ignore templates patterns taken from https://github.com/github/gitignore

The repository has been cloned inside the scanner project to avoid cloning it each time the scanner is run. It will need to be occasionally updated to support new languages or frameworks.

The --exclude-from-templates option is repeatable, each value correspond to a keyword which is the prefix to the filename with .gitignore extension. The list of available templates is displayed in the help screen and also in the error message when a given template does not exists.