age plugin support

[flokli]

Summary

age v1.2.0 got released, exposing a plugin package providing an age plugin client:

The Go module now exposes a plugin package that provides an age plugin client. That is, Recipient and Identity implementations that invoke a plugin binary, allowing the use of age plugins in Go programs.

gopass should be able to make use of this.

Already mentioned by @dominikschulz in https://github.com/gopasspw/gopass/issues/2059:

Once age v1.1.0 comes with plugin support I'd like to support that, too. So people can use their hardware tokens (at least YubiKeys) with gopass+age.