[Resource Groups](https://gitlab.com/gitlab-org/gitlab/-/issues/15536) is a useful way to limit the concurrency of pipeline jobs. However, the MVC is limiting both in terms of the number of resource groups a pipeline job can use a.k.a. Multiple exclusive locks (currently a single job can use one resource group), and concurrency (a resource group can only have one job run at a time, but some resources may have more) This epic captures the way we can improve the usefulness of resource groups by making them more flexible.