Correctly separating dev H2 db and prod postgres db

[NorDar]

For development and testing a h2 in memory db should be used. For production a posgres db should be used.

One of the problems is that spring in their unending dark wizar-dreary ways breaks itself when importing h2 and postgres dependencies at the same time. Experiments with two different build files work locally but break as soon as they are rebuilt and deployed to GAE.

This means we now inject a different build definition during deployment.

[NorDar]

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One sets the environment variable to spring_profiles_active=local for local development and spring_profiles_active=gcp for GAE deployment. GH Actions will replace the file accordingly during deployment.