Possible filter material options should be obtained from HDF5 file

[rajanplumley]

https://github.com/pcdshub/hxr-attenuator/blob/dabdc3f68ebb032dda78351d8f71b7ef66c6d46f/caproto/ioc-satt-dev/db/filters.py#L17

[klauer]

Doing best-effort calculations with periodictable and code-level override for now. I think this is probably good to close.