Check dataset connection before migration job (and other apps)
Before starting the services (api, admin) and workers, we ensure the database is accessible and the assets directory (if needed) exists.

In the case of the migration job: if the database cannot be accessed, we skip the migration, to avoid blocking Helm


Fixes #763. Replaces #767. Depends on #791.

Check dataset connection before migration job (and other apps): Before starting the services (api, admin) and workers, we ensure the database is accessible and the assets directory (if needed) exists.

In the case of the migration job: if the database cannot be accessed, we skip the migration, to avoid blocking Helm


Fixes #763. Replaces #767. Depends on #791.
