Use "onion site" instead of "onionsite"
In #41655 (comment 2962774) we decided to avoid "onion service" in favour of "onion site", to be a bit more specific to the browser context.
However, for the neterror and two other strings we use "onionsite" without the space. We should probably stick to one convention: "onion site" or "onionsite". Any preferences?
My guess would be "onion site" is clearer, so we should change the strings to use that.