Footer: generate "policy" links from config

[chalin]

For the moment, the footer "policy" links are hardcoded (#660). They should instead be generated -- like other other .Site.Params.links such as user and developer -- from a similar list.

grpc.io/config.yaml

Lines 50 to 64 in 1782ee7

	links:
	user:
	- name: Twitter
	url: https://twitter.com/grpcio
	icon: fab fa-twitter
	- name: Google Groups
	url: https://groups.google.com/g/grpc-io
	icon: fab fa-google
	- name: Gitter
	url: https://gitter.im/grpc/grpc
	icon: fab fa-gitter
	developer:
	- name: GitHub
	url: https://github.com/grpc
	icon: fab fa-github