Feature Request: Add TTL support to keys

[ftKnox]

Have you considered adding support for setting TTL values on keys? Would be nice to have this. Maybe via something like:

func (s *Store) InsertTTL(key, data interface{}, ttl time.Duration) {...}
func (s *Store) UpdateTTL(key, data interface{}, ttl time.Duration) {...}
func (s *Store) UpsertTTL(key, data interface{}, ttl time.Duration) {...}

Ref: https://github.com/dgraph-io/badger#setting-time-to-livettl-and-user-metadata-on-keys

[killswitch-GUI]

This would be amazing.

[PD-Pramila]

Any update on adding this TTL feature on keys?
Also, are there any plans to add:

1. Metadata on keys and then supporting that metadata value to filter search results.
2. Batch processing.