404 handling broken

[MortenHofft]

@MattBlissett It seems something has changed in the way we handle 404s
They do not show the dedicated 404 page anymore

prod: https://data.dissco-uk.org/tester
staging: https://cartagena-botanical-garden.hp.gbif-staging.org/tester

but some also work: https://beaty-biodiversity-museum.hp.gbif-staging.org/tester

[MattBlissett]

The Beaty Museum has a 404.html page, which is what the sites are configured to use: hp-beaty-biodiversity-museum/404.html

Cartagena has a directory: hp-cartagena-botanical-garden/404/index.html

It's a global configuration shared by all the sites, so ideally we use the same thing everywhere.

[MortenHofft]

I cannot force them to be the same as the editors can change it as well, but I can add an explicit url to the 404's and hope they do not get overwritten. Currently they differ because of the _config. In theory we could also normalize that with an additional file that defined how permalinks should use. Without or without .html
Let me start by simply making them all the same to begin with

[MortenHofft]

Could we have a fallback to the fallback? It is a thing that is easy to change but hard to notice when doing changes in Jekyll