feat: Extend list of PdgParticles particles to include Pb (#2042)

When the particle to collide is set to Pb `acts.PdgParticle.lead` the pythia invokes a HI collisions generator. 
This way one can test ACTS in this conditions by invoking the generator like this:
```python
  addPythia8(
        s,
        npileup=1,
        beam=acts.PdgParticle.lead, # lead
        cmsEnergy=5.0*u.TeV,
        vtxGen=acts.examples.GaussianVertexGenerator(
            stddev=acts.Vector4(0.0125 * u.mm, 0.0125 * u.mm, 55.5 * u.mm, 5.0 * u.ns),
            mean=acts.Vector4(0, 0, 0, 0),
        ),
        rnd=rnd,
        outputDirRoot=outputDir
    )
``` 
That should help with studies in needed for: #1778
Tagging @pbalek

Core/include/Acts/Utilities/PdgParticle.hpp

@@ -30,6 +30,7 @@ enum PdgParticle : int32_t {
   eAntiNeutron = -eNeutron,
   eProton = 2212,
   eAntiProton = -eProton,
+  eLead = 1000822080
 };
 
 /// Convert an anti-particle to its particle and leave particles as-is.

Examples/Python/src/Base.cpp

@@ -226,7 +226,8 @@ void addPdgParticle(Acts::Python::Context& ctx) {
       .value("eNeutron", Acts::PdgParticle::eNeutron)
       .value("eAntiNeutron", Acts::PdgParticle::eAntiNeutron)
       .value("eProton", Acts::PdgParticle::eProton)
-      .value("eAntiProton", Acts::PdgParticle::eAntiProton);
+      .value("eAntiProton", Acts::PdgParticle::eAntiProton)
+      .value("eLead", Acts::PdgParticle::eLead);
 }
 
 void addAlgebra(Acts::Python::Context& ctx) {

Examples/Python/tests/test_base.py

@@ -12,7 +12,7 @@ def test_logging():
 
 
 def test_pgd_particle():
-    assert len(acts.PdgParticle.__members__) == 16
+    assert len(acts.PdgParticle.__members__) == 17
 
 
 def test_algebra():