Ensure that there are always available builders for AlmaLinux

[javihernandez]

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