RT-5.7: Test is modified to use ENCAP only nexthop which is not PoPGate requirement

[bkreddy143]

Test has been modified to use ENCAP only next hop which is mixing requirements from two different projects.

https://github.com/openconfig/featureprofiles/blob/main/feature/interface/aggregate/otg_tests/aggregate_all_not_viable_test/aggregate_all_not_forwarding_viable_test.go#L1039

if ENCAP only next-hop is must requirement test needs to be split and update the README accordingly. Other option could be , just add gRIBI route with NHs the is supported in the first project and validate the forwarding-viable feature .