feat(ci): add metrics snapshot to tailsampling E2E workflow

[hharshhsaini]

Which problem is this PR solving?

• Resolves part of Implement framework to validate backwards compatibility of metrics #6278

Description of the changes

• Add verify-metrics-snapshot action step to ci-e2e-tailsampling.yml
• Update tailsampling_test.go to pass "tailsampling" as the storage
  label to e2eInitialize() instead of "memory", so the snapshot is
  written to .metrics/metrics_snapshot_tailsampling.txt with a unique
  name that does not conflict with the memory workflow's snapshot
• The metrics scraping itself is already handled automatically by
  E2EStorageIntegration.scrapeMetrics() in e2e_integration.go the
  test just needed the correct label and the workflow step wiring

How was this change tested?

• Verified that testTailSamplingProccessor uses e2eInitialize() from
  E2EStorageIntegration, which already calls scrapeMetrics() at cleanup
• Confirmed the pattern matches existing workflows (badger, memory, grpc, etc.)
  that call verify-metrics-snapshot after the same test framework
• gofmt passes on all modified Go files

Checklist

• I have read https://github.com/jaegertracing/jaeger/blob/main/CONTRIBUTING_GUIDELINES.md
• I have signed all commits
• I have added unit tests for the new functionality
• I have run lint and test steps successfully: make lint test

AI Usage in this PR (choose one)

See AI Usage Policy.

• None: No AI tools were used in creating this PR
• Light: AI provided minor assistance (formatting, simple suggestions)
• Moderate: AI helped with code generation or debugging specific parts
• Heavy: AI generated most or all of the code changes

[Copilot]

Pull request overview

This PR updates the tail sampling processor integration tests to capture and verify metrics snapshots. It makes two coordinated changes: updating the test to use "tailsampling" as the identifier for metrics snapshots, and adding the metrics snapshot verification step to the CI workflow.

Changes:

• Changed the storage parameter in the tail sampling test from "memory" to "tailsampling" to provide a distinct metrics snapshot identifier for tail sampling tests
• Added metrics snapshot verification step to the tail sampling CI workflow

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cmd/jaeger/internal/integration/tailsampling_test.go	Updated storage parameter to "tailsampling" for metrics snapshot naming
.github/workflows/ci-e2e-tailsampling.yml	Added metrics snapshot verification step to match the test's metrics snapshot identifier

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.66%. Comparing base (6275e86) to head (8886bc1).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8190      +/-   ##
==========================================
- Coverage   95.67%   95.66%   -0.02%     
==========================================
  Files         317      317              
  Lines       16750    16750              
==========================================
- Hits        16026    16024       -2     
- Misses        571      572       +1     
- Partials      153      154       +1     

Flag	Coverage Δ
badger_v1	9.05% <ø> (ø)
badger_v2	1.04% <ø> (ø)
cassandra-4.x-v1-manual	13.25% <ø> (ø)
cassandra-4.x-v2-auto	1.03% <ø> (ø)
cassandra-4.x-v2-manual	1.03% <ø> (ø)
cassandra-5.x-v1-manual	13.25% <ø> (ø)
cassandra-5.x-v2-auto	1.03% <ø> (ø)
cassandra-5.x-v2-manual	1.03% <ø> (ø)
clickhouse	1.16% <ø> (ø)
elasticsearch-6.x-v1	16.83% <ø> (ø)
elasticsearch-7.x-v1	16.86% <ø> (ø)
elasticsearch-8.x-v1	17.01% <ø> (ø)
elasticsearch-8.x-v2	1.04% <ø> (ø)
elasticsearch-9.x-v2	1.04% <ø> (ø)
grpc_v1	7.79% <ø> (ø)
grpc_v2	1.04% <ø> (ø)
kafka-3.x-v2	1.04% <ø> (ø)
memory_v2	1.04% <ø> (ø)
opensearch-1.x-v1	16.91% <ø> (ø)
opensearch-2.x-v1	16.91% <ø> (ø)
opensearch-2.x-v2	1.04% <ø> (ø)
opensearch-3.x-v2	1.04% <ø> (ø)
query	1.04% <ø> (ø)
tailsampling-processor	0.52% <ø> (ø)
unittests	94.35% <ø> (-0.02%)	⬇️

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[yurishkuro]

why is this needed? what problem does it solve?

[hharshhsaini]

why is this needed? what problem does it solve?

@yurishkuro This PR is part of #6278 which aims to collect metrics snapshots from all E2E integration test workflows for backwards compatibility tracking.

The tailsampling integration test already runs the full Jaeger v2 binary with the tail sampling processor active via E2EStorageIntegration.e2eInitialize(), so e2e_integration.go automatically scrapes the Jaeger metrics endpoint and writes them to .metrics/ but the workflow was never wired up to call verify-metrics-snapshot, meaning those artifacts were never uploaded or compared against the baseline.

The tail sampling processor registers its own metrics (e.g. processor_tail_sampling_*) that do not appear in any storage-backend tests (memory, badger, etc.), so a dedicated snapshot is important to catch backwards-incompatible changes to those metrics.

We also updated the storage label from "memory" to "tailsampling" to give the snapshot a distinct file name (metrics_snapshot_tailsampling.txt) instead of shadowing the memory workflow's snapshot.