feat: make config property protected to enable inheritance

BREAKING CHANGE: Changed `config` property from private to protected to allow
subclasses to access internal state. This enables better extensibility but
may affect consumers who subclass DrupalJsonApiParams.

- Changed `private config` to `protected config` in DrupalJsonApiParams class
- Allows subclasses to access and modify internal config state
- Improves library extensibility for advanced use cases

Author: d34dman

src/index.ts

@@ -71,7 +71,7 @@ export class DrupalJsonApiParams implements DrupalJsonApiParamsInterface {
 
   protected qsOptions: object = {};
 
-  private config: DrupalJsonApiParamConfig = {
+  protected config: DrupalJsonApiParamConfig = {
     useShortCutForQueryGeneration: true,
     alwaysUseFieldNameForKeys: false,
   };