DB change to differentiate containers and keys on secrets

[raildo]

Nowadays, containers and keys are stored in the same table, the only difference between this two entities is that a container have an empty value in the DB. To have a more robust solution, we should create a new flag or use PRAGMA on sqlite to distinguish between them.

[simo5]

If we can distinguish between a NULL value and an empty value that may also be sufficient, we cannot have keys with a NULL value, keys have at a minimum an empty value.

[simo5]

But I think the interface we used may not be able to carry None (NULL) so that may be the issue and what we need to fix.

[simo5]

(The other issue is upgrading the db schema)