Allow up to 3 levels of subcategories

[robe]

Discourse by default allows at most 2 levels of subcategorization. This reasoning is mostly in there because it was deemed "It's good for you", to prevent people from shooting themselves in the foot having needlessly nested hierarchies.

But I think we SHOULD shoot ourselves in the foot, at least a little-bit.

So I am proposing we up this to 3 categories.

That way we can have maybe a Projects -> project_name -> project_name - developers group :) (or not, keep projects not as base category).

But anyway this feature was suggested in #3144

and in reviewing:

​https://meta.discourse.org/t/is-it-possible-to-create-sub-subcategories/13821/17

It seems possible to do with SiteSetting.max_category_nesting = 3

[robe]

I did in staging -- ​https://discourse.staging.osgeo.org

​https://discourse.staging.osgeo.org/c/organizing-committees/13

And on the hope page the 3 level category looks like this

[robe]

Now done in prod as well so we can have 3 levels of categories

Had to enter the container and set the setting as detailed below

cd /var/discourse/

./launcher enter import

rails c

SiteSetting.max_category_nesting = 3
quit

There doesn't seem to be a place in the UI to do this or at least I couldn't find it. Guess cause they want to discourage it and it's probably still experimental.

I also didn't add this to import.yml or app.yml cause I couldn't see anything like a SiteSetting, so I assume these settings are only in the database which is why the change took affect immediately without restarting the app.