Tracking issue for no-index-update

### Summary

Original issue: #3479
Implementation: #4990
Documentation: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#no-index-update
Issues: https://github.com/rust-lang/cargo/labels/Z-no-index-update

### Unresolved Issues
- [ ] Will this ever be stabilized? Added for crater, which may be content with unstable.