Add config discovery support to envoy

[martavicentenavarro]

What does this PR do?

Adds config discovery support to the Envoy integration: a from_ports discovery strategy on port 8001 with two candidates covering both the OpenMetrics (openmetrics_endpoint) and legacy (stats_url) dispatch modes, regenerated config models, auto_conf.yaml, get_e2e_discovery_metadata() wiring in the E2E fixture, and new test_e2e_discovery / test_e2e_discovery_all_candidates E2E tests.

Known limitation: the legacy /stats candidate is restricted (via discovery_overrides.py) to the hinted admin port (8001), since probing arbitrary exposed ports with /server_info + /stats risks misidentifying an unrelated upstream as Envoy's admin endpoint. Envoy deployments exposing the admin interface on a different port won't be discovered via the legacy path and still require a hand-written static config. openmetrics_endpoint keeps the default fallback across all candidate ports.

Motivation

Part of the config discovery rollout (DSCVR-484). This is a fresh implementation built with the restructured create-discovery-pr skill, superseding #24121 which was built with the older version of the workflow.

Related work: #24121 (older implementation) has been closed in favor of this PR.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add qa/required if this PR needs QA validation, or qa/skip-qa if it does not. Exactly one of the two is required.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[datadog-datadog-prod-us1-2]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 70.07% (-18.22%)

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[dd-octo-sts]

Validation Report

All 21 validations passed.

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Validation	Description	Status
agent-reqs	Verify check versions match the Agent requirements file	✅
ci	Validate CI configuration and code coverage settings	✅
codeowners	Validate every integration has a CODEOWNERS entry	✅
config	Validate default configuration files against spec.yaml	✅
dep	Verify dependency pins are consistent and Agent-compatible	✅
http	Validate integrations use the HTTP wrapper correctly	✅
imports	Validate check imports do not use deprecated modules	✅
integration-style	Validate check code style conventions	✅
jmx-metrics	Validate JMX metrics definition files and config	✅
labeler	Validate PR labeler config matches integration directories	✅
legacy-signature	Validate no integration uses the legacy Agent check signature	✅
license-headers	Validate Python files have proper license headers	✅
licenses	Validate third-party license attribution list	✅
metadata	Validate metadata.csv metric definitions	✅
models	Validate configuration data models match spec.yaml	✅
openmetrics	Validate OpenMetrics integrations disable the metric limit	✅
package	Validate Python package metadata and naming	✅
qa-label	Validate the pull request declares whether it needs QA for the next Agent release	✅
readmes	Validate README files have required sections	✅
saved-views	Validate saved view JSON file structure and fields	✅
version	Validate version consistency between package and changelog	✅

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