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.

---

For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/bazel-contrib/setup-bazel/issues/67?shareId=XXXX-XXXX-XXXX-XXXX).

config.js

@@ -53,6 +53,15 @@ if (diskCacheEnabled) {
   }
 }
 
+const diskCacheFilesConfig = core.getMultilineInput('disk-cache-files')
+let diskCacheFiles = [
+  '**/BUILD.bazel',
+  '**/BUILD'
+]
+if (diskCacheFilesConfig.length > 0) {
+  diskCacheFiles = diskCacheFilesConfig
+}
+
 const repositoryCacheConfig = core.getInput('repository-cache')
 const repositoryCacheEnabled = repositoryCacheConfig !== 'false'
 let repositoryCacheFiles = [
@@ -140,8 +149,7 @@ module.exports = {
     enabled: diskCacheEnabled,
     files: [
       ...repositoryCacheFiles,
-      '**/BUILD.bazel',
-      '**/BUILD'
+      ...diskCacheFiles
     ],
     name: diskCacheName,
     paths: [bazelDisk]