CPAlgorithms: user-side improvement for PtEtaSelectionBlock

In case users schedule multiple PtEtaSelection blocks on the same object container, they must name the decoration using the selectionDecoration option. But they are also adding these pT/eta selections to different object selections, via selectionName. So we can simplify the config from the user point of view by internally naming the pT/eta selection after selectionName. The option selectionDecoration is therefore set to None by default and can be used for overriding this naming convention (expert mode).

For instance, in:

Muons:
  - containerName: 'AnaMuons'
    WorkingPoint:
      - selectionName: 'loose'
        quality: 'Medium'
        isolation: 'NonIso'
      - selectionName: 'tight'
        quality: 'Medium'
        isolation: 'Tight_VarRad'
    PtEtaSelection:
      - selectionName: 'loose'
        selectionDecoration: 'selectPtEta_loose'
        minPt: 10000.0
        maxEta: 2.5
      - selectionName: 'tight'
        selectionDecoration: 'selectPtEta_tight'
        minPt: 25000.0
        maxEta: 2.5

with this MR the last part can be simplified to:

    PtEtaSelection:
      - selectionName: 'loose'
        minPt: 10000.0
        maxEta: 2.5
      - selectionName: 'tight'
        minPt: 25000.0
        maxEta: 2.5

and the selectPtEta_loose/selectPtEta_tight have been created internally and appended to loose/tight.