Open requested to merge mspalla/athena:KLFforTTbb into 21.2
Implementation of KLFitter for all-had ttbb analysis. An existing version of our iterative KLFitter implementation had been already merged into 21.2. After the merge, we had to adjust our implementation further so that the pseudo-continuous b-tagging is used for ordering jets prior to the KLFitter run. In the previous version, the b-tagging weight was used for jet ordering, which was deprecated by the flavour tagging group. The ordering using pseudo-continuous b-tagging is added as an additional option.