firebase-ios-sdk

Migrate from using IID SDK for Remote Config to the new FIS SDK (#5096)

* Update podspec to replace IID with installations SDK.

* Update sample app podfile to include installations sdk.

* Source code changes to support migration to FIS. The FIS SDK now supports multi-app FIS ids and tokens.

* Update RC test app to use FIS SDK.

* WIP: Unit tests for incorporating FIS with Remote Config.

* Remote Config: fix Installations tests (#5109)

* Fix Installations tests.

* Fix Firebase/Auth version (#5106)

* Remote Config: enable ARC for tests.

* run ./scripts/style.sh

* Fix warnings

* Remote Config: enable ARC for tests. (#5108)

* Remote Config: enable ARC for tests.

* run ./scripts/style.sh

* Fix warnings

Co-authored-by: Paul Beusterien <paulbeusterien@google.com>

* Add the installations token as an HTTP header.

* Add changelog for FIS changes.

Co-authored-by: Maksym Malyhin <mmaksym@google.com>
Co-authored-by: Paul Beusterien <paulbeusterien@google.com>