query output duplicates 'entities' header for each batch

[ththvseo]

one would expect that '''query''' produces an output file that can be read back by '''upsert'''.
this does not work, because query will duplicate the '''entities:'' key for each batch, essentially writing a corrupt yaml file.
(for yaml, but i guess other formats are similarly affected, it's probably a similiar issue for json, but i have not tried; for csv it likely does not cause issues because there is no header?)

even worse, upsert will accept such a yaml file as input, but apparently only use the last batch (because the parser internally overwrites repeating keys?)
but that is probably not a bug in dsio itself, because the yaml parser is from a library and not part of dsio.)

[nshmura]

Thanks!
This is a bug, I will fix this issue.