feat: extend conditionNames

This allows consumers to set their own considitionNames and have sass pick this up.

Examples:

Supporting a single entrypoint but targeting multiple themes
```scss
@use 'my-design-tokens';

.class {
  color: my-design-tokens.$color-1
}
```

package.json
```json
{
  "name": "my-design-tokens",
  "exports": {
      ".": {
        "sass": {
          "theme1": "./path-to-theme1.scss",
          "theme2": "./path-to-theme2.scss"
          }
      }
   }
}
```
Webpack config
```
module.exports = {
  resolve: {
    conditionNames: [someFlag ? "theme1" : "theme2", "..."]
  }
}
```

src/utils.js

@@ -530,7 +530,7 @@ function getWebpackResolver(
   const webpackModuleResolve = promiseResolve(
     resolverFactory({
       dependencyType: "sass",
-      conditionNames: ["sass", "style"],
+      conditionNames: ["sass", "style", "..."],
       mainFields: ["sass", "style", "main", "..."],
       mainFiles: ["_index", "index", "..."],
       extensions: [".sass", ".scss", ".css"],
@@ -541,7 +541,7 @@ function getWebpackResolver(
   const webpackImportResolve = promiseResolve(
     resolverFactory({
       dependencyType: "sass",
-      conditionNames: ["sass", "style"],
+      conditionNames: ["sass", "style", "..."],
       mainFields: ["sass", "style", "main", "..."],
       mainFiles: ["_index.import", "_index", "index.import", "index", "..."],
       extensions: [".sass", ".scss", ".css"],