Add support for more encondings

MR needs to be updated.

(Minor title typo fix.)

As mentioned over in ✨ Add Western Europe ISO-8859-15 encoding to csv export data Postponed we need this feature to land here first before we can offer the UI to select an encoding.

I suppose it would be nice if there was a way to get a list of valid encodings that we could present a UI for.

Also, you should decide if you want to accept utf8 or utf-8 since the code at the moment sort of uses both.