moss: Add auto-prune feature to delete old states or enforce a retention limit

[raphaelreichart]

Users should be able to configure moss to automatically prune stored states using one of the following settings:

• Automatically delete states older than a specified age (e.g. delete states older than 30 days based on their creation date).
• Retain only a configured maximum number of states, when the limit is exceeded, delete the oldest states first.

This would help manage disk usage while still allowing users to keep states as long as needed.

Additional feature: Allow users to tag specific states so they are excluded from automatic deletion.