[PWGJE] Adding bkg indexing to jetCorrelationD0 task

[MattOckleton]

Removing matchedFrom and selectedAs columns and replacing with category which will be filled with an int corresponding to the signal, reflection, or correlated background.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 13 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 3d5c4cc at 2026-08-05 16:25:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 4 errors and 0 warnings.'
Found 4 errors and 0 warnings.
++ [[ 4 -gt 0 ]]
++ cat /sw/BUILD/16061fda2edb41e1380861752521d94e541bec02/O2Physics-code-check/errors.txt
PWGJE/Tasks/jetCorrelationD0.cxx:39:1: error: included header type_traits is not used directly [misc-include-cleaner,-warnings-as-errors]
PWGJE/Tasks/jetCorrelationD0.cxx:42:10: error: inclusion of deprecated C++ header 'math.h'; consider using 'cmath' instead [modernize-deprecated-headers,-warnings-as-errors]
PWGJE/Tasks/jetCorrelationD0.cxx:370:11: error: implicit conversion 'unsigned long long' -> 'bool' [readability-implicit-bool-conversion,-warnings-as-errors]
PWGJE/Tasks/jetCorrelationD0.cxx:372:18: error: implicit conversion 'unsigned long long' -> 'bool' [readability-implicit-bool-conversion,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 4 -gt 0 ]]
++ exit 1
--

Full log here.