Add gitignore for GoogleService-Info.plist (#7178)

* Add secret to performance integration tests.

* Updat pull request path to trigger the GHA.

* Remove pull request condition.

* Remove dev test App GoogleService-Info.plist

* Create README.md

* Fix style.

* Add gitignore for GoogleService-Info.plist.

* Move .gitignore to root directory.

Author: jeremyjiang-dev

.gitignore

@@ -35,6 +35,9 @@ FirebaseSegmentation/Tests/Sample/GoogleService-Info.plist
 # FirebaseMLModelDownloader integration tests GoogleService-Info.plist
 FirebaseMLModelDownloader/Tests/Integration/Resources/GoogleService-Info.plist
 
+# FirebasePerformance dev test App and integration tests GoogleService-Info.plist
+FirebasePerformance/**/GoogleService-Info.plist
+
 Secrets.tar
 
 # OS X