Ensure that there are always available builders for AlmaLinux

Right now, the build scheduler is dispatching whatever gets into the system to build nodes without taking into account whether it's a community product or the AlmaLinux product.

In order to avoid the situation where all build nodes are busy building packages for community products, we need to implement a mechanism to keep some builders free, just in case AlmaLinux developers need to build something. This is specially critical in `exotic` arches such as s390x, since we do not have that many build nodes for such architecture.

AC:
* There is a configurable rate limit that ensures that we keep some builders for AlmaLinux product
* When reaching the rate limit for community products, skip dispatching community product builds to build nodes until we're below the limit