Automate renewal of self-signed test certificate

[tido64]

Description

The self-signed test certificate expired but luckily we caught it during nightly builds. We should investigate whether we can automate the renewal process. For now, a new certificate has been created and a reminder is set up in #385.

Your environment

• react-native-test-app version: 0.6.8
• Tested platforms:
  • Android
  • iOS
  • macOS
  • Windows