TTL topic page needed

[zuiderkwast]

There is no overview page about TTL (time-to-live) and key expiry.

The best introduction we have is in commands/expire.md, but this is just one of the commands about TTL.

We need an overview page with an introduction to time-to-live and links to all commands that are related to it (expire, pexpire, persist, ttl, pttl, getex, setex, restore).