[PWGLF] add process function to look for pe+e- findable candidates

[fmazzasc]

@hfribert

[github-actions]

O2 linter results: ❌ 2 errors, ⚠️ 1 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for f3f2b3d at 2026-08-07 18:06:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 11 errors and 0 warnings.'
Found 11 errors and 0 warnings.
++ [[ 11 -gt 0 ]]
++ cat /sw/BUILD/d8813cd68719dda83c45535ee915544aaaf46128/O2Physics-code-check/errors.txt
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:58:8: error: constructor does not initialize these fields: ccdb [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:99:3: error: no header providing "o2::framework::Produces" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:102:3: error: no header providing "o2::framework::Service" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:109:42: error: no header providing "o2::framework::OutputObjHandlingPolicy" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:115:13: error: no header providing "o2::framework::InitContext" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:134:11: error: no header providing "o2::framework::AxisSpec" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:148:40: error: no header providing "o2::framework::kTH1F" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:167:82: error: no header providing "o2::framework::kTH2F" is directly included [misc-include-cleaner,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:685:5: error: uninitialized record type: 'pProton' [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:686:5: error: uninitialized record type: 'pGamma1' [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
PWGLF/TableProducer/Strangeness/sigmaplusbuilder.cxx:877:5: error: use auto when initializing with a template cast to avoid duplicating the type name [modernize-use-auto,-warnings-as-errors]
++ [[ 0 -gt 0 ]]
++ [[ 11 -gt 0 ]]
++ exit 1
--

Full log here.