Replace packngo with metal-go

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What problem are you facing?

https://github.com/equinix-labs/metal-go is an OAS3 generated SDK that is the successor to the hand curated https://github.com/packethost/packngo SDK.

The latter is being deprecated once key integrations including this project, CPEM, kubernetes-sigs/cluster-api-provider-packet#527, and terraform-provider-equinix have successfully adopted the new SDK (thus proving its completeness and accuracy).

Related to equinix-labs/metal-go#99

How could the Equinix Metal CLI help solve this problem?

Convert the following to metal-go:

• 2fa Two-factor Authentication operations: receive, enable, disable.
• capacity Capacity operations: get, check
• device Device operations: create, get, update, delete, reinstall, start, stop, and reboot.
• event Events operations: get.
• facilities Facility operations: get.
• gateway Metal Gateway operations: create, delete, and retrieve.
• hardware-reservation Hardware reservation operations: get, move.
• init Create a configuration file.
• ip IP address, reservations, and assignment operations: assign, unassign, remove, available, request and get.
• metros Metro operations: get.
• operating-systems Operating system operations: get.
• organization Organization operations: create, get, update, payment-methods, and delete.
• plan Plan operations: get.
• port Port operations: get, convert, vlans.
• project Project operations: create, get, update, delete, and bgpenable, bgpconfig, bgpsessions.
• ssh-key SSH key operations: create, get, update, and delete.
• user User operations: get and add.
• virtual-network Virtual network (VLAN) operations : create, get, delete.

[displague]

Moving to #333