cubicweb #2713671 fine-tune logging & lower the amount of ldapfeed related logs [validation pending]

with many users this can make the log grow very fast; also some logging looks inapropriate

prioritynormal
typebug
done in3.17.7
load0.200
load left0.000
closed by#6afdeaabac74 [ldapparser] demote some logs from warning to debug (closes #2713671)
patch[ldapparser] demote some logs from warning to debug (closes #2713671) [applied]