linter: Support negations in overrides

This syntax would be very useful in an override:

```
      "files": ["packages/services/**", "!packages/services/**/*.test.ts"],
      "rules": {
        "no-restricted-imports": [
          "error",
          {
            "patterns": [
              {
                "group": [
...snip...
```

Currently it doesn't seem to work. 