Added SNS4SNS end-to-end test scenario (not automated)

src/tests/sns4sns24/01-tfs-topology.json

src/tests/sns4sns24/02-ietf-l3vpn-nbi.json

src/tests/sns4sns24/02-tfs-l3-service.json

src/tests/sns4sns24/clab-cli-r1.sh

src/tests/sns4sns24/clab-cli-r2.sh

src/tests/sns4sns24/clab-deploy.sh

src/tests/sns4sns24/clab-destroy.sh

src/tests/sns4sns24/clab-inspect.sh

src/tests/sns4sns24/deploy_specs.sh

src/tests/sns4sns24/ietf-create.sh

src/tests/sns4sns24/ietf-delete.sh

src/tests/sns4sns24/ietf-get.sh

src/tests/sns4sns24/sns4sns.clab.yml

src/tests/sns4sns24/static_setup/r1-static.cfg

src/tests/sns4sns24/static_setup/r2-static.cfg

src/tests/sns4sns24/static_setup/sns4sns.clab.yml

src/tests/sns4sns24/static_setup/static-setup.txt