[Jobs Match Making] Implement job prioritization logic

[aldbr]

Description

Among the matching jobs returned by the prototype, select a single job. The spec defines prioritization criteria: job type ordering, running limits, owner/group round-robin, and FIFO as tiebreaker.

The production data shows why this matters: lbprods/lhcb_mc owns ~80% of jobs. Without fair scheduling, other owners would be starved.

Priority configuration should be loadable from a file.

Definition of Done

• Given matching jobs + running counts + configuration, return a single job
• Job type priority from configuration
• Running limits per (site, job_type)
• Owner and group round-robin
• FIFO as final tiebreaker
• Integration test: simulate repeated matching calls and verify fair distribution across owners