RootStorageSvc: Clean-up and reorganize RootDatabase options

I noticed this issue in the full-chain MC RNTuple ART tests. In PoolReadConfig we explicitly set a TREE_CACHE size for the input event data. This causes an error on the RootDatabase side when reading an input file that has RNTuple instead of TTree. This MR implement a practical workaround to avoid this specific problem so that the log scanning won't mark the jobs as failing.

Looking at PoolReadConfig at large, we have a lot of hard-coded TTree and/or CollectionTree specific operations. As we move forward we should make these more flexible for RNTuple usage. For that I created ATEAM-948.

cc: @gemmeren