[PWGUD] Add deuteron in UPC task

[m-rasa]

Add new task for the study of deuteron production in UPC collisions.
CMakeList file modified to include the new task.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 47 warnings, 🔕 0 disabled

[alibuild]

Error while checking build/O2Physics/code-check for 19685df at 2026-10-04 21:22:

## sw/BUILD/O2Physics-code-check-latest/log
--
========== List of issues found ==========
++ echo 'Found 1 errors and 2 warnings.'
Found 1 errors and 2 warnings.
++ [[ 1 -gt 0 ]]
++ cat /sw/BUILD/3642724a42d20fb3d6ef032a3d1ce6f1b67a7f87/O2Physics-code-check/errors.txt
PWGUD/Tasks/sgDeuteronSpectra.cxx:110:24: error: no header providing "TMath::Abs" is directly included [misc-include-cleaner,-warnings-as-errors]
++ [[ 2 -gt 0 ]]
++ cat /sw/BUILD/3642724a42d20fb3d6ef032a3d1ce6f1b67a7f87/O2Physics-code-check/warnings.txt
PWGUD/Tasks/sgDeuteronSpectra.cxx:98:5: warning: do not declare C-style arrays, use 'std::array' instead [modernize-avoid-c-arrays]
PWGUD/Tasks/sgDeuteronSpectra.cxx:105:11: warning: implicit conversion 'int' -> 'bool' [readability-implicit-bool-conversion]
++ [[ 1 -gt 0 ]]
++ exit 1
--

Full log here.