Overriding Run Numbers in Component Accumulator based configuration

This merge request depends on !37700 (merged). It introduces two new ConfigFlags:

acf.addFlag('Input.OverrideRunNumber', False )
acf.addFlag('Input.TimeStamp', lambda prevFlags : [] if not prevFlags.Input.OverrideRunNumber else GetInitialTimeStampsFromRunNumbers(prevFlags.Input.RunNumber))

GetInitialTimeStampsFromRunNumbers finds the timestamps corresponding to a given MC RunNumber - this functionality is copied from RunDMCFlags.py in the old-style configuration.
A new module Control/AthenaKernel/python/EventIdOverrideConfig.py is added to handle the configuration of the EvtIdModifierSvc. Currently this only supports overriding all events in a job to have the same RunNumber, which is sufficient for the standard simulation use-cases, but this part of the code would need to be extended to properly support pile-up digitization configuration and data overlay input simulation configuration.
Database/AthenaPOOL/AthenaPoolCnvSvc/python/PoolReadConfig.py is extended to configure the EventSelector differently and to configure EvtIdModifierSvc when ConfigFlags.Input.OverrideRunNumber==True.

Discussed in the Core Software Meeting a few weeks ago.