Move m_glo/m_ghi init to .cpp

Try to address NVHPC 24.1 linker issue:
```
/usr/bin/ld: lib/libwarpx.3d.MPI.CUDA.DP.PDP.OPMD.PSATD.EB.QED.a(BTD_Plotfile_Header_Impl.cpp.o): in function `BTDPlotfileHeaderImpl::BTDPlotfileHeaderImpl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
/home/runner/work/WarpX/WarpX/Source/Diagnostics/BTD_Plotfile_Header_Impl.cpp:26: undefined reference to `amrex::Vector<std::array<double, 3ul>, std::allocator<std::array<double, 3ul> > >::~Vector()'
```

Author: ax3l

Source/Diagnostics/BTD_Plotfile_Header_Impl.H

@@ -144,9 +144,9 @@ private:
     /** Number of Fabs in the plotfile. */
     int m_numFabs;
     /** Lower corner physical coordinates of each fab in the plotfile. */
-    amrex::Vector<amrex::Array<amrex::Real, AMREX_SPACEDIM> > m_glo {{AMREX_D_DECL(0.,0.,0.)}};
+    amrex::Vector<amrex::Array<amrex::Real, AMREX_SPACEDIM> > m_glo;
     /** Upper corner physical coordinates of each fab in the plotfile. */
-    amrex::Vector<amrex::Array<amrex::Real, AMREX_SPACEDIM> > m_ghi {{AMREX_D_DECL(1.,1.,1.)}};
+    amrex::Vector<amrex::Array<amrex::Real, AMREX_SPACEDIM> > m_ghi;
     std::string m_CellPath;
 
 };

Source/Diagnostics/BTD_Plotfile_Header_Impl.cpp

@@ -22,7 +22,9 @@
 using namespace amrex::literals;
 
 BTDPlotfileHeaderImpl::BTDPlotfileHeaderImpl (std::string const & Headerfile_path)
-    : m_Header_path{Headerfile_path}
+    : m_Header_path{Headerfile_path},
+      m_glo{{AMREX_D_DECL(0., 0., 0.)}},
+      m_ghi{{AMREX_D_DECL(1., 1., 1.)}}
 {
 
 }