Typing: Add type annotations to vo.py

[rdimaio]

#6454

On the # type: ignore change: the error log ignored by this message is this one:

Found 1 new problems in /home/runner/work/rucio/rucio/lib/rucio/daemons/automatix/automatix.py
  - 1 errors with message """Argument of type "Unknown | str | None" cannot be assigned to parameter "vo" of type "str" in function "map_vo"
                               Type "Unknown | str | None" cannot be assigned to type "str"
                                 "None" is incompatible with "str"""".
    Candidates: line 169

I tried a few fixes, but the issue is that that portion of code assumes that client.vo is not None, even though it might be. A functional change needs to be done to fix that logic. We can do this at a later point, when handling the # type: ignore comments.