LRMS-wide default benchmark to store in the AAR if per-job data is missing

It is turned out that people are struggling from benchmark settings.

The current approach is to store benchmark as a historical job accounting attribute instead of put some static value during the publishing. The approach is still correct, but in technical implementation there are jobs that miss the benchmark value for various (including not yet identified) reasons in .diag file.

This changeset aimed to fulfill the requirement to have a default (also fallback) value for the benchmark set if one is missing in the .diag. It is still during AAR creation (instead of publishing time), so consistent with entire accounting implementation.

The new option goes to [lrms] as we don't have any common accounting block.

Chengeset will allow to implement mitigation for BUGZ-3921.