CircleCI requires to be configured to hold the secrets used to push to Google Cloud.

We want to pull our containers to our Google Cloud project, so we need a service account with those persmissions to be configured in our CircleCI project.

1. Read CircleCI guide about how to configure Google Cloud Service Accounts in CircleCI
2. Read Google guide about the permissions that the Google Cloud Service Account need to have to push into a Google Cloud Container Registry. We will need to give permission of "Storage Admin" role.
3. Read Google guide about how to push container images to a Google Cloud Container Registry.