Wait for database before starting core app

[ppawlowski]

Description

When using the helm chart to install the app with local database support, the application may restart a couple of times:

NAME                        READY   STATUS    RESTARTS      AGE
flowforge-d64cf667b-pqfnm   1/1     Running   2 (44s ago)   49s
flowforge-postgresql-0      1/1     Running   0             49s

The reason for such behavior is application container starts quicker than the database one.

{"level":"ERROR","time":"2023-11-21T13:41:48.471Z","msg":"Failed to start: SequelizeConnectionRefusedError: connect ECONNREFUSED 10.96.94.235:5432"}
ConnectionRefusedError [SequelizeConnectionRefusedError]: connect ECONNREFUSED 10.96.94.235:5432

It will be nice to start the main app only once the database is up and ready to handle requests.
A possible solution is to use an init container which will check database availability.