Re-label references to HW injections in documentation to not use GW designation

Created by: cosmiccommunitydonates

For example, on this documentation page: https://gwpy.github.io/docs/latest/examples/table/rate_binned.html

Strictly speaking, there is no GW event 'GW100916' and referring to this HW inject as a GW on a public page might cause confusion.

Suggestion: relabel with 'HW' or 'HWinj' designation.