Add a HEALTHCHECK to the images

When helping people on StackOverflow, I often see people having problems with Docker Compose and applications that try to connect to the database immediately on startup. When using a simple docker compose 'depends_on' directive, compose only waits for the database to be started before starting the application. The application then fails because the database isn't ready to accept connections yet.

The solution is to add a healthcheck to the database container in docker compose and have the application wait for the database to enter a healthy state.

It would be nice if the healthcheck was included in the Postgres image by default. A simple HEALTHCHECK ["pg_isready"] should be enough.

Inizia individuando le definizioni delle immagini Docker per le immagini Postgres e verificando come vengono create le relative varianti. Aggiungi in modo coerente l’healthcheck richiesto, quindi verifica che Docker Compose possa attendere che il database segnali uno stato integro prima di avviare l’applicazione.