Add sFlow Egress Sampling test README

[alexmihoc-google]

This PR adds the test requirements (README.md) for SFLOW-2: sFlow Egress Sampling Configuration and Verification.

While standard sFlow sampling captures packets at the ingress pipeline, egress sFlow enables sampling of packets as they egress the device (post-encapsulation and routing header modifications). This test qualifies OpenConfig configuration, operational state telemetry, and flow sample verification for interface-level egress sampling on supported platforms.

Key Coverage

• Test ID: SFLOW-2
• Testbed: topologies/atedut_2.testbed
• OpenConfig Paths Covered:
  • /sampling/sflow/interfaces/interface/config/egress-sampling-rate
  • /sampling/sflow/interfaces/interface/state/egress-sampling-rate
  • /sampling/sflow/interfaces/interface/state/enabled
  • Global sFlow collector and enablement paths (/sampling/sflow/config/enabled, etc.)
• Test Scenarios:
  • SFLOW-2.1: Configure interface-level egress sampling rate via gNMI Replace and verify telemetry state.
  • SFLOW-2.2: Transmit data traffic through the DUT and verify that captured sFlow datagrams report the correct egress output interface (ifIndex) and adhere to the configured sampling rate.
  • SFLOW-2.3: Disable egress sampling and verify clean teardown.

[OpenConfigBot]

Pull Request Functional Test Report for #6025 / 64beee2

Virtual Devices

Device	Test	Test Documentation	Job	Raw Log
Arista cEOS		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Cisco 8000E		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Cisco XRd		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Juniper ncPTX		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Nokia SR Linux		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Openconfig Lemming		SFLOW-2: sFlow Egress Sampling Configuration and Verification

Hardware Devices

Device	Test	Test Documentation	Raw Log
Arista		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Cisco		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Juniper		SFLOW-2: sFlow Egress Sampling Configuration and Verification
Nokia		SFLOW-2: sFlow Egress Sampling Configuration and Verification

Help

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces the documentation and registry entry for the SFLOW-2 test case, which focuses on verifying egress sFlow sampling on network devices. The changes outline the required OpenConfig paths, testbed topology, and verification procedures for ensuring that egress-sampled packets are correctly captured and reported by the DUT.

Highlights

• New Test Documentation: Added a comprehensive README for the SFLOW-2 test case, covering egress sFlow sampling configuration, telemetry validation, and traffic verification.
• Test Registry Update: Registered the new SFLOW-2 test case in the global test registry to include it in the test suite tracking.

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[gemini-code-assist]

Code Review

This pull request introduces the test plan for SFLOW-2 (sFlow Egress Sampling Configuration and Verification) and registers it in the test registry. The review feedback highlights a syntax error in the protobuf registry file (using tests { instead of test: {) and a repository style guide violation where the test plan document should be named README.md instead of sflow_egress_test_README.md.