*: Refine the notion of a configured VRF in FRR

*: Refine the notion of a configured VRF in FRR

Refine the notion of what FRR considers as "configured" VRF. It is no longer
based on user just typing "vrf FOO" but when something is actually configured
against that VRF. Right now, in zebra, the only configuration against a VRF
are static IP routes and EVPN L3 VNI. Whenever a configuration is removed,
check and clear the "configured" flag if there is no other configuration for
this VRF. When user attempts to configure a static route and the VRF doesn't
exist, a VRF is created; the VRF is only active when also defined in the
kernel.

Updates: 8b73ea7bd479030418ca06eef59d0648d913b620
Signed-off-by: Vivek Venkatraman <vivek@cumulusnetworks.com>
Reviewed-by:   Donald Sharp <sharpd@cumulusnetworks.com>
Reviewed-by:   Don Slice <dslice@cumulusnetworks.com>
Ticket: CM-10139, CM-18553
Reviewed By: CCR-7019
Testing Done:
1. Manual testing for L3 VNI and static routes - FRR restart, networking
restart etc.
2. 'vrf' smoke

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