[PWGDQ] Simplify the DQ UPC event selection

[sigurdnese]

• Remove legacy process function
• The filterPbPb task now only produces the DQRapidityGapFilter table
• The DQRapidityGapFilter now only contains two columns: The filter bitmap itself, and the index (as a uint64_t) of the new BC found by the SGSelector
• In the tableMaker, the ZDC tables and histograms are filled with the values from that new BC, when the process function using the DQRapidityGapFilter is run
• The DQRapidityGapFilter does not actually remove any events when running tableMaker, the event selection should instead be done by using cuts on the appropriate quantities (e. g. kIsSingleGapA)
• The process function used for UPC event selection now includes occupancy estimator calculation

[github-actions]

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