Check if the database exists/is accessible in the migration job
In some cases, the migration job can be run (in k8s) while the mongo database does not exist. In that case, it fails and the install/upgrade is blocked.

As the database does not need to be migrated if it does not exist yet, we should test if we can access the database, and if not, return with a success without doing anything.

found by @rtrompier 
Check if the database exists/is accessible in the migration job: In some cases, the migration job can be run (in k8s) while the mongo database does not exist. In that case, it fails and the install/upgrade is blocked.

As the database does not need to be migrated if it does not exist yet, we should test if we can access the database, and if not, return with a success without doing anything.

found by @rtrompier 