Add support for Metal VRF Routes

[displague]

What problem are you facing?

With #268 there are a few features of VRF yet to be implemented. Among them is VRF Routes configuration.

https://github.com/equinix-labs/metal-go/blob/main/docs/VRFsApi.md

Method	HTTP request	Description
CreateVrfRoute	Post /vrfs/{id}/routes	Create a VRF route
DeleteVrfRouteById	Delete /routes/{id}	Delete a VRF Route
FindVrfRouteById	Get /routes/{id}	Retrieve a VRF Route
GetVrfRoutes	Get /vrfs/{id}/routes	Retrieve all routes in the VRF
UpdateVrfRouteById	Put /routes/{id}	Update a VRF Route

How could the Equinix Metal CLI help solve this problem?

metal vrf routes-create --vrf-id {vrf_id}
metal vrf routes-update --route-id {route_id}
metal vrf routes-get --route-id {route_id}
metal vrf routes-delete --route-id {route_id}

One of these two ids should probably be "id" as an argument. Use whatever the current convention is for subcommands with IDs and when we use the short "id" vs the subcommand prefix.

[codinja1188]

/assign @codinja1188