SRC plugins incompatible with Ubuntu 22.04 + sram auth?

[sverhoeven]

See https://gitlab.com/rsc-surf-nl/plugins/plugin-nginx/-/issues/1

Also the SRC Jupyter catalog items now use SRAM for auth see September 2023 section on https://servicedesk.surf.nl/wiki/display/WIKI/SRC+New+features . We should check that the JupyterHub installation inside the eWatercycle component (aka this repo) still authz with local posix users so we can add users without having visitors go through SRAM.

[sverhoeven]

Until plugin is fixed we use Ubuntu 20.04 as base image.