[wght] Should we have named instances for wght 1, 1000, maybe 50?

https://github.com/googlefonts/axisregistry/blob/main/Lib/axisregistry/data/weight.textproto has only 9x named instances for 100 to 900, which maybe is correct for "API fallbacks", but we have fonts (including Roboto Flex, Recursive, Nunito, Mulish, Cairo, Cairo Play and others coming along) already with weight 1000, and (Hepta Slab, etc) with weight 1.

@evanwadams this is something to consider for future ways to enumerate named instances in the weight axis.