Add option to scan a specific repo

[elad-pticha]

For now, We support two options

1. Scanning a specific organization
2. Scanning the entire GitHub by star counts

We need an option to scan a specific repo in case organizations have a large number of repositories.

Let's take as an example the scan organization flow:

We get all the repos in an organization and then send them to download_workflows_and_actions.

By implementing this issue, we can create a new function called: download_repo_workflows_and_actions that will get a single repo (or a list of repos) to be scanned.

[oreenlivnicode]

Big Like.
Maybe it should be under the download org mode?
You will pass --org-name and --repo-name

[anerdwithaknife]

Since the organization isn't strictly needed for a single repo I think implementing it as a separate mode is more straightforward from a usage perspective.

I have taken a stab at it and opened a PR as a starting point: #118