Add flag to toggle use of digital ROT creation (and include other changes from...

Add flag to toggle use of digital ROT creation (and include other changes from egamma fix in 21.0). Using this will save some CPU, but currently does not give optimal egamma performance - see ATLASRECTS-3949, ATLASRECTS-4573.

Set false by default for egamma tuning until GXF changes can be made to fully support use of PRDs properly.

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