[PWGCF] Add configurable flags for ITS layer selection

[Luzhiyongg]

No description provided.

[github-actions]

O2 linter results: ❌ 0 errors, ⚠️ 2 warnings, 🔕 5 disabled

[alibuild]

Error while checking build/O2Physics/o2 for edad2ea at 2026-04-22 16:42:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGCF/Flow/Tasks/flowTask.cxx:1422:25: error: loop variable 'trptEta' creates a copy from type 'const std::pair<float, float>' [-Werror=range-loop-construct]
ninja: build stopped: subcommand failed.

Full log here.

[Luzhiyongg]

Error while checking build/O2Physics/o2 for edad2ea at 2026-04-22 16:42:

## sw/BUILD/O2Physics-latest/log
/sw/SOURCES/O2Physics/slc9_x86-64-slc9_x86-64/0/PWGCF/Flow/Tasks/flowTask.cxx:1422:25: error: loop variable 'trptEta' creates a copy from type 'const std::pair<float, float>' [-Werror=range-loop-construct]
ninja: build stopped: subcommand failed.

Full log here.

This has been fixed by the latter commit.
MacOS error is something unrelated.

[alibuild]

Error while checking build/O2Physics/o2 for 9356c10 at 2026-04-23 18:18:

No log files found

Full log here.