This is not possible with native HTML, therefore you won't find any straightforward DokuWiki plugins for it either.
There is a more complex and inflexible solution with CSS counters (similar to
numbered headings), but there is nothing in DokuWiki using this as far as I'm aware.
There are some plans to have something more sophisticated in CSS (like
markers and
@counter-style) but that's still further ahead in the future and not properly implemented by any browsers yet.