Add dummy certificates to PushApi authenticator and test apps to
simplify their usage:
Bug: 33046496
Test: manual tests.
Change-Id: I94e5fa1ac430da77c0f74ed87bd12467a3ba76b8
Refactor push api test apps to have more similar code and use another
manifest entry.
Bug: https://b.corp.google.com/issues/33046496
Test: none
Change-Id: I2c87ccae0e73892eb15fb3e6f98bbb7372e0a24a