Add disk-cache-files input to support multiple modules

Fixes #67

Add support for overriding disk cache files for multiple modules in the repository.

* Add a new input `disk-cache-files` in `action.yml` to specify custom disk cache files.
* Update `config.js` to handle the new `disk-cache-files` input and override the `diskCache.files` array if provided.
* Update the documentation in `README.md` to include the new `disk-cache-files` input and provide examples of its usage.

---

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README.md

@@ -111,6 +111,27 @@ Default `false`.
   ```
 </details>
 
+### `disk-cache-files`
+
+Specify custom disk cache files.
+
+Default `""`.
+
+<details>
+  <summary>Examples</summary>
+
+  #### Override disk cache files
+
+  ```yaml
+  - uses: bazel-contrib/setup-bazel@0.13.0
+    with:
+      disk-cache-files: |
+        **/BUILD.bazel
+        **/BUILD
+        custom/path/BUILD
+  ```
+</details>
+
 ### `external-cache`
 
 Cache `external/` repositories based on contents of `MODULE.bazel` and `WORKSPACE` files.