[API spec] Rename input schemas of create API request body

[rinzler-17]

Renaming should be done for:

1. VrfCreateInput, CreateVrfRequest
2. MetalGatewayInput, VrfMetalGatewayCreateInput
3. VrfIPReservationCreateInput, IPReservationRequestInput

[displague]

What are your proposals for the renames:

• IPReservationRequestInput -> IPReservationCreateInput
• CreateVrfRequest -> VrfCreateInput
• MetalGatewayInput -> MetalGatewayCreateInput
• VrfMetalGatewayCreateInput -> (already conventional)

Others to be aware of:

• BgpConfigRequestInput.
• TransferRequestInput
• SupportRequestInput

In these examples "Request" may indicate that the resource is not Created but updated or returned as a report. In other cases (Support), Request creates a clause as SupportRequest, rather than acting as a modifier for Input - RequestInput.