Reduce the number of concurrent cache jobs by ~2x

The limit was not conservative enough.

Also add a CMake cache property to enable controling the limit manually.

added Build enhancement labels

assigned to @rmatev

/ci-test --platforms=x86_64_v2-centos7-gcc12+detdesc-opt

added ci-test-triggered label

added RTA label

• [2023-04-20 13:54] Validation started with lhcb-master-mr#7660

resolved all threads

approved this merge request

merged

mentioned in commit c1224c08

mentioned in issue #563 (closed)