Frr upstream now has yang support and a new mgmt daemon

[ITJamie]

Frr upstream now supports yang and more sensible automation features.

Consideration should be made to rebase and move sonic away from templated config files/vtysh.

Refs:

http://docs.frrouting.org/projects/dev-guide/en/latest/mgmtd-dev.html

https://docs.frrouting.org/en/latest/mgmtd.html

[kcudnik]

please elaborate more