Conditional select menus (pulldowns, LinkML enums, etc)

[turbomam]

NMDC use case:

In addition to the MIxS environmental triad of EnvO terms, NMDC also describes the origin of biosamples with 5-part GOLD paths.

Interactive GOLD paths explorer: https://gold.jgi.doe.gov/ecosystemtree?mode=organism

Journal article: https://www.researchgate.net/publication/328539814_Genomes_OnLine_database_GOLD_v7_updates_and_new_features

There are thousands of valid combinations of the five GOLD path ranks, so we don't want to build one pre-composed pulldowns. Therefore we have one pulldown for each rank. But you can't mix the values of the five ranks indiscriminately. They have to form valid paths, like

1. Ecosystem Category → Terrestrial
2. Ecosystem → Environmental
3. Specific Ecosystem → Agricultural land
4. Ecosystem Type → Soil
5. Ecosystem Subtype → Clay

We would like a selection from Ecosystem Category to constrain the values available in the columns for Ecosystem and lower ranked