roadmap.md

* Packet->Equinix Metal rename #6901 

Updates throughout to reflect #6901 renaming for Packet to Equinix Metal.

* Rename Packet to Equinix Metal throughout the project #6901

Packet is renamed to Equinix Metal in more contexts including
documentation links. The Terraform provider used is still the Packet
provider. The environment variables and configuration options still
refer to the Packet name.

Signed-off-by: Marques Johansson <mjohansson@equinix.com>

Co-authored-by: Edward Vielmetti <ed@packet.net>