[PWGCF] FemtoUniverse V0 Task -- changed combinations policy for v0v0 and improved v0 duplicates check

[Eloviyo]

• For V0-V0 case : changed from "CombinationsFullIndexPolicy" to "CombinationsStrictlyUpperIndexPolicy" - it solves the problem of empty same event histograms for non-identical v0 pairs.
• Modified V0 Duplicates function: implemented invariant mass check for each particle pair rejected by the v0 pair cleaner - it helps with the statistics as previously both these particles were rejected while now it keeps one of the v0 which has invariant mass closer to the default value.