Add feature to release the smart card context on timeout

[ava1ar]

I am using my Yubikey for both GPG and yubikey-agent and trying to find a descent workaround for the https://github.com/go-piv/piv-go/issues/47 issue. I am fine to loose the PIN caching (I can use libsecret to store the pin for me on the machine I trust) and killall -HUP yubikey-agent workaround kind of works, except this command needs to be issued manually. Can we add functionality to release the smart card context on timeout after last key access? This would allow to me configure context auto-release and make yubikey-agent and gpg-agent co-existence a bit easier.

[jcharaoui]

Now that I've migrated by OpenPGP keys to the Yubikey, I find it very inconvenient to have to manually release the exclusive locks when switching between SSH and OpenPGP tasks, for example when signing a commit (PGP) then pushing a branch to a remote (SSH).

Unless this can be fixed somehow, I'm thinking of either moving to FIDO-based SSH keys or using gpg-agent SSH key support.