Warning when using deprecated server types

[jooola]

Description

Server types may be deprecated over time, packer should report warning to the users that are using deprecated warning to make sure they get surprised once they are marked as unavailable.

Consider using https://pkg.go.dev/github.com/hetznercloud/hcloud-go/v2/hcloud/exp/deprecationutil for computing the deprecation messages.

[jooola]

The images deprecation may also be computed using the deprecationutil in hcloud-go, streamlining the deprecation warnings.