Add hdf_archive dataset append feature

[ye-luo]

Then we can get rid of direct calls

../src/QMCDrivers/WalkerLogBuffer.h:      h5d_append(f.top(), "data", file_pointer, buffer.dim(), dims, buffer.data());
../src/QMCHamiltonians/ObservableHelper.h:  /// "file pointer" for h5d_append
../src/QMCHamiltonians/ObservableHelper.cpp:    h5d_append(file.top(), "value", current, rank, mydims.data(), first_v + lower_bound);
../src/Estimators/TraceManager.h:      h5d_append(f.top(), "traces", file_pointer, buffer.dim(), dims, buffer.data());