Exclude legacy recipes from gallery

[lukruh]

I just realized, that archived legacy recipes are still part of the gallery and listed in the sidebar on top level. It's good to have them easy findable in the documentation, but maybe its not the first one we want to expose to potential new users. The list of recipes keeps growing and at some point we might want to reconsider which figures we want to expose in the gallery. Any thoughts/opinions?

In case we want to exclude them from gallery: My suggestion would be to move the documentation files for legacy recipes in a legacy or archive subfolder (similar to recipes and diagnostics) and exclude this folder in the generate gallery script. The legacy recipes can also be grouped in the sidebar. Alternatively we could just add a IGNORED_FILES list to the script.

[bettina-gier]

I'd agree on the subfolder, so the sidebar navigation is cleaner, but maybe also move the other recipes in subfolders according to their categories in the current index.rst