Implement retry until success for restore_api_key() call in CTS test

[aseure]

Because of the way Algolia is designed, performing a restoreApiKey may not
succeed because the previous deleteApiKey takes some time to get propagated
to all Algolia servers, giving us the following response: [404] Key already exists.

To prevent that, we need to change the testApiKeys CTS test, if implemented,
to retry even on [404] Key already exists response.

[chloelbn]

Closing as PHP client doesn't implement CTS