HLT: Move DB connection managment from Psc to HltEventLoopMgr

Merged Frank Winklmeier requested to merge fwinkl/athena:fork_sleep into master

Move the management of DB connections before forking from the Psc to HltEventLoopMgr (ATR-8907). This allows the sleep time to be configured via the new dbConnIdleWaitSec property.

Moved the actual code to the TrigRDBManager helper class so we don't have to change the friend relationship in IRDBAccessSvc in case we need to move this code somewhere else again.

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