`uv init` ignores workspace when `--isolated` flag is used (#5290)
## Summary
Per https://github.com/astral-sh/uv/pull/5250#issuecomment-2242137762
> It would also be great to have an argument (perhaps leveraging the
global isolated option) that allows us to disable workspace discovery
when we don't want to add a project as a member.
## Test Plan
```sh
$cargo run -- init work
$ cargo run -- init work/pkg-a --isolated
warning: `uv init` is experimental and may change without warning
Initialized project sub-c in /tmp/work
```
