Add sample nmstate manifest for br-ex with 1 port

[mkowalski]

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[openshift-ci]

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[openshift-ci]

@mkowalski: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-metal-ipi-bm	ae96835	link	true	/test e2e-metal-ipi-bm
ci/prow/e2e-metal-ipi-serial-ovn-ipv6	ae96835	link	false	/test e2e-metal-ipi-serial-ovn-ipv6

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