Add easy way to turn off / set compression and compression threshold in hdf5

[mclarsen]

Its unclear under what the cost of compression is. It would be nice to be able to change the default compression threshold (or set it to infinity to turn it off). This would allow us to empirically determine when we want to do it and not to do it.

[cyrush]

We have a conduit example that shows a subset of the hdf5 options:

https://llnl-conduit.readthedocs.io/en/latest/relay_io.html#hdf5-i-o-options

We need to wire the up the existing options the relay hdf5 extract ing Ascent.