Prune expires_at tokens

[iruoy]

Closes #384

This still requires the sanctum.expiration to be set.

[driesvints]

Actually I was thinking that we might be able to do this without requiring sanctum.expiration to be set? Maybe we should always allow pruning by expired_at and if sanctum.expiration is set additionally prune by created_at?

[iruoy]

That is how I envisioned it before looking at the code. However I didn't want to make the change before getting some feedback. I'll look into it later today.

[iruoy]

I've pushed some changes. Tokens with expired_at will now always be pruned and I've used the new artisan task() component.

I've kept the warn() component for now, but I think it should be removed.

[driesvints]

@iruoy you're sure that tokens without an expired_at timestamp won't be deleted, right?