Create an example of PCE using BGP-LS

[watal]

Create spec.yaml for PCE using BGP-LS in "pola/examples".
Leave the existing "pola/examples/sr-mpls_l3vpn/" as a TED disable example.

[Motok1]

If FRR is to be used, it is not possible because FRR does not currently have a BGP-LS implementation

[pguibert6WIND]

If FRR is to be used, it is not possible because FRR does not currently have a BGP-LS implementation

Is there an opensource implementation that would permit to send BGP LS messages, based on an hexadecimal stream, for instance?

[watal]

@pguibert6WIND We have yet to learn of any implementation with a hexadecimal stream, but there is GoBGP as an implementation that can be input via gRPC.
GoBGP's BGP-LS gRPC API has just been implemented, so some functionality may need to be added. Also, input via GoBGP CLI (gobgp global rib add -a ls) is not currently supported.