ci: configure GitHub Actions to use integration_test package (#8910)

[russellwheatley]

• Add integration_test.dart

• Add dummy e2e_test.dart file

• Add integration_test package

• Run integration tests for every pull request

• Use IntegrationTestWidgetsFlutterBinding.ensureInitialized();

• Format & use flutter test

• Use multidex

• Add new line for FlutterMultiDexApplication.java

• Format to pass CI

• Add comment for flutter drive command

• Use flutter test command for macos test

• Format test command for android

• Use one line comment

• Re-trigger CI

• Re-trigger CI

• Bump minSdkVersion to 21 for tests app## Description

Replace this paragraph with a description of what this PR is doing. If you're modifying existing behavior, describe the existing behavior, how this PR is changing it, and what motivated the change.

Related Issues

Replace this paragraph with a list of issues related to this PR from the issue database. Indicate, which of these issues are resolved or fixed by this PR. Note that you'll have to prefix the issue numbers with flutter/flutter#.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.

[nilsreichardt]

Description for this PR:

## Description

The `integration_test` package is the new way to write e2e tests. Therefore, this PR migrates the tests from driver tests to integration tests.

ToDos:

- [ ] Update description for this PR
- [ ] Update title of the PR to "test: migrate all packages from driver tests to integration tests"
- [ ] Migrate `cloud_firestore`
- [x] Migrate `cloud_functions`
- [x] Migrate `firebase_analytics`
- [x] Migrate `firebase_app_installations`
- [x] Migrate `firebase_auth`
- [x] Migrate `firebase_core`
- [x] Migrate `firebase_crashlytics`
- [x] Migrate `firebase_database`
- [x] Migrate `firebase_dynamic_links`
- [x] Migrate `firebase_in_app_messaging`
- [ ] Migrate `firebase_ml_model_downloader`
- [ ] Migrate `firebase_remote_config`
- [x] Migrate `firebase_messaging`
- [ ] Migrate `firebase_storage`
- [ ] Migrate `firebase_firestore_odm`
- [ ] Migrate `firebase_performance`
- [ ] Delete driver tests (test_driver/ folder)
- [ ] Remove `drive` as dependency
- [ ] Mark `drive` dependency on pub.dev as discontinued?
- [ ] Check if CI is flaky (run CI 50 times)
- [ ] Update docs on how to run integration tests

As side effect we see that the Android CI e2e tests pipeline is way more stable.

## Related Issues

Closes #8909

## Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes (`[x]`).
This will ensure a smooth and quick review process. Updating the `pubspec.yaml` and changelogs is not required.

- [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
- [x] My PR includes unit or integration tests for *all* changed/updated/fixed behaviors (See [Contributor Guide]).
- [x] All existing and new tests are passing.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] The analyzer (`melos run analyze`) does not report any problems on my PR.
- [x] I read and followed the [Flutter Style Guide].
- [x] I signed the [CLA].
- [x] I am willing to follow-up on review comments in a timely manner.

## Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

- [ ] Yes, this is a breaking change.
- [x] No, this is *not* a breaking change.

<!-- Links -->
[issue database]: https://github.com/flutter/flutter/issues
[Contributor Guide]: https://github.com/firebase/flutterfire/blob/master/CONTRIBUTING.md
[Flutter Style Guide]: https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[pub versioning philosophy]: https://dart.dev/tools/pub/versioning
[CLA]: https://cla.developers.google.com/

[nilsreichardt]

Will be continued in #9230