Make isort's `detect-same-package` behavior configurable (#6833)
## Summary
Our first-party import detection uses a heuristic that doesn't exist in
isort: if an import appears to be from within the same package as the
containing file, we mark it as first-party. For example, if you have a
directory `./foo/__init__.py`, and you import `from foo import bar` in
`./foo/baz.py`, we'll mark that as first-party. (See:
https://github.com/astral-sh/ruff/pull/1266.)
This is often unnecessary, and arguably should be removed (though it
does have some important use-cases that are otherwise unserved -- I
believe Dagster uses it to ensure that all packages mark imports from
within the same package as first-party, but not imports _across_
different first-party packages)... but it does exist, and it does help
in cases in which the `src` field is not properly configured.
This PR adds an option to turn off this behavior:
```toml
[tool.ruff.isort]
detect-same-package = false
```
This is being introduced to help codebases migrating over from isort
that may want more consistent behavior with their current sorting.
## Test Plan
`cargo test`
