[PWGJE] Add PCH for JET tasks

[singiamtel]

Heavily speeds up compilation

CC @ktf

[github-actions]

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

[fjonasALICE]

what is the time difference in compilation that you observe? should we consider this for other JE tasks too? also, are there some other headers that do not frequently change in O2Physics that we should consider precompiling?

[ktf]

@singiamtel very nice. Could you share numbers on the improvement? How does it handle changes in the framework headers? Will it actually notice and recompile? That's where the previous attempt I had did not converge.

[aalkin]

This is great, together with my changes at the framework level this will reduce the compilation times very significantly. However, I suggest restructuring this to make it more transparent for the end users, we do not want to rewrite every CMakeLists.txt in O2Physics. We can introduce a convention on the "central" target for each PWG, that collects all the universal headers and then update o2physics_add_dpl_workflow to automatically use it.

[ktf]

@vkucera on a separate note, could we please make sure the O2 linter does not tell people to change QA to Qa ?