GaudiConfig2: minor performance optimizations for Configurable

• replace .format with f-strings (a few in non-critical places were left where readability is better)
• replace setattr with direct _properties access in merge

Non of these are earth-shattering but they did show up in ATLAS profiles.

changed milestone to %v37r1

added lhcb-gaudi-head label

• [2023-10-20 00:03] Validation started with lhcb-gaudi-head#3721
• [2023-10-20 00:12] Validation started with lhcb-run2-gaudi-head#635
• [2023-10-20 00:21] Validation started with lhcb-sim10-gaudi-head#415
• [2023-10-20 00:36] Validation started with lhcb-gaudi-head#3721

approved this merge request

merged

mentioned in commit 19d07bb0