Report correlation between pre-and-post DRT STA

[donn]

Description

The RC values are not a universal fit for all designs (because of differences in congestion, layer utilization, and so on), so there may be a large discrepancy between pre and post DRT STA.

Proposal

It may be a good idea after running post-PNR STA to use https://github.com/The-OpenROAD-Project/OpenROAD-flow-scripts/blob/master/flow/util/correlateRC.py to provide suggested RC values for future runs of the same design.