remoting: Adjust prompt level for dev server prompts (#11440)

This changes the remoting prompts to use `PromptLevel::Warning` instead
of `PromptLevel::Destructive`.
In #11015 we decided to apply PromptLevel::Destructive to prompts other
than the new path picker. However, we did not notice that this breaks
confirmation with the keyboard, so it should really only be used in
specific situations (e.g. replacing a file with the remote "save as"
picker, because it matches the behavior of the macOS file dialog).

Release Notes:

- N/A