HFInvMassFitter refactory

[lubynets]

• Replace namesOfBkgPdf etc with std::array
• Reduce code repetition in fit results table printing
• Reduce code repetition due to alias for Range() here
• Use enums for switch-case here etc.
• Use enums for hFitConfig bins
• Refactor setFixedValue lambda-function
• Read optional json fields also optionally (e.g. do not require meanFile if fixMean == false)
• Check that config vector size is equal to nSliceVars (or empty)
• Get rid of warnings with -Wall -Wextra - done by Vit
• Get rid of RooFit warnings
• throw std::runtime_error() instead of return -1, e.g. here
• Close opened files
• Factor out open file and get object with check for nullptr into functions
• Leave only one constructor
• Get rid of unnecessary (?) cloning, e.g. here
• Pass here hMassForRefl (?) Do not create hMassFor... histograms for rebinning, rebin the existing histogram;
• Fix Warning in <TH2F::LabelsOption>: Axis xaxis has no labels!
• Fix bug (logical error) with fitting selected ranges (e.g. "SBL, SBR") in Chi2 mode
• Exclude mBkgPdfPrefit from class members, move it under the if-statement block
• Factor out repeating code here and here
• HFInvMassFitter: ClassDef->ClassDefOverride
• Move > 1 line function definitions from .h to .cxx
• Solve signedness problem of iSliceVar

[lubynets]

Major part implemented in the AliceO2Group#14339.
Solving the bug with ranges selection in the Chi2 mode is postponed for future investigation.