Merge branch 'addMergeFlag' into '21.0'

Introduce new rec flag to designate AOD-merging jobs and use it

See merge request atlas/athena!7445

(cherry picked from commit 1d51307d [formerly fe2adf31])

e7456c2c add new rec-flags doMerging, should help in reducing spurious DB connections in merging jobs
ecf2d9b8 don't set up DB connections in merging jobs
296cb481 don't load (some) conditions in merging jobs
41e05411 explicitly disable AODFix in POOL-file merging
57353b65 do not initialize unecessary tools for merging jobs + don't load associated conditions
5065ece2 add AthFile/impl to excludeTracePattern
243a6cde set merging flag only for AOD-merging jobs
423e30b5 rename flag rec.doMerging -> rec.doAODMerging
c8aa013a fix typo

Former-commit-id: c5b1d712