Opening file for writing in append mode on inexistant file fails

I normally write in append mode when I want to append my error traces as to not erase every different threads messages into a file. Calling open in append on an inexistant file works in python and doesn't trigger an error. I can't see why this isn't supported and would need help understanding.

The code that seems to cause the issus is the following ;
``` python
if not exists_on_cloud and any(m in mode for m in ("r", "a")):
raise CloudPathFileNotFoundError(
f"File opened for read or append, but it does not exist on cloud: {self}"
)
```

Opening a file for writing in general seems supported.

My suggestion is to support "append" mode so as to give a nice feature for everybody, but I understand I may be missing something here. If I'm missing something indeed, then I would instead align the behaviour to block local append mode through the library as to avoid surprise in production environment where append mode might be blocked.

Start at the cloud-path open logic containing the shown exists_on_cloud and mode check, then compare its append handling with the existing write behavior and open-mode tests. Resolve whether append should create a missing cloud file or remain blocked, and cover the chosen behavior with a regression test.

Written by the indexing model from the issue text.