Add new option skip_security_updates_on_concurrent_limit

If the concurrent limit is reached based on the number to `number_of_concurrent_updates`, we do not want it to block any security package updates. Thus, I suggest providing a new option to let those who need to override the default Violinist value skip security updates, too, even if the concurrent limit when has been reached.

PR:
- Config: https://github.com/violinist-dev/violinist-config/pull/28
- Docs: https://github.com/violinist-dev/docs/pull/44