message: ADIOS2 output switch material to MFEM attribute in CellData
  To sync up with ParaViewDataCollection
diff: @@ -298,7 +298,7 @@ void adios2stream::Print(const Mesh& mesh, const mode print_mode)
  element_nvertices = static_cast<size_t>(mesh.elements[0]->GetNVertices());
  }
  SafeDefineVariable<uint64_t>(io, "connectivity", {}, {}, {nelements, element_nvertices+1});
  - SafeDefineVariable<int32_t>(io, "material", {}, {}, {nelements});
  + SafeDefineVariable<int32_t>(io, "attribute", {}, {}, {nelements});
  // vertices
  SafeDefineVariable<uint32_t>(io,"NumOfVertices", {adios2::LocalValueDim});
  @@ -351,7 +351,7 @@ void adios2stream::Print(const Mesh& mesh, const mode print_mode)
  (var_connectivity);
  adios2::Variable<int32_t> var_element_attribute =
  - io.InquireVariable<int32_t>("material");
  + io.InquireVariable<int32_t>("attribute");
  adios2::Variable<int32_t>::Span span_element_attribute = engine.Put<int32_t>
  (var_element_attribute);
  @@ -435,7 +435,7 @@ void adios2stream::Print(const Mesh& mesh, const mode print_mode)
  engine.Put<uint64_t>(varConnectivity);
  adios2::Variable<int32_t> varElementAttribute =
  - io.InquireVariable<int32_t>("material");
  + io.InquireVariable<int32_t>("attribute");
  // zero-copy access to adios2 buffer to put non-contiguous to contiguous memory
  adios2::Variable<int32_t>::Span spanElementAttribute =
  engine.Put<int32_t>(varElementAttribute);
  @@ -720,7 +720,7 @@ std::string adios2stream::VTKSchema() const noexcept
  vtkSchema += R"(
  </Points>
  <CellData>
  - <DataArray Name="material" />
  + <DataArray Name="attribute" />
  </CellData>
  <Cells>
  <DataArray Name="connectivity" />
  