[vpp repo] Update make go-api-files procedure in VPP repo

[ondrej-fabry]

In the VPP repository there is a make target go-api-files for generating Go bindings for VPP binary API from the local API files in the source code. The make target simply executes a Python script generate_go.py that runs go install to get the GoVPP binapi-generator. However it uses some arbitrary commit of GoVPP with the old import path git.fd.io/govpp.git that used before migration to GitHub.

The VPP repository should only use released versions of GoVPP.

Tasks:

• [ ] update to new import path go.fd.io/govpp
• [ ] replace global variable DefaultGoVppCommit=xxx with DefaultGoVppVersion=v0.6.0
• [ ] replace the install procedure for GoVPP for Go older than 1.18 (which is the minimum version) with error "unsupported Go version, please install Go 1.18 or newer"

[fatelei]

assign to me

[sknat]

This could also include updating the documentation page on VPP itself at e.g. https://s3-docs.fd.io/vpp/23.02/interfacing/go/index.html