test(ffe): pin end-to-end scenario to remote config

[leoromanovsky]

Motivation

The FEATURE_FLAGGING_AND_EXPERIMENTATION end-to-end scenario delivers feature flag configuration through Remote Configuration. Java now defaults the Feature Flags configuration source to agentless, so leaving the source implicit prevents Java from subscribing to FFE_FLAGS and causes /ffe evaluations to time out while waiting for initial configuration.

Working on in-development: DataDog/dd-trace-java#11892

Changes

• Set DD_FEATURE_FLAGS_CONFIGURATION_SOURCE=remote_config in the legacy FFE end-to-end scenario.
• Keep the dedicated agentless configuration-source tests on their mocked agentless backend.

Decisions

• Pin the delivery mode at the scenario boundary because these tests explicitly exercise Remote Configuration behavior.
• Preserve agentless as the SDK default; no Java behavior changes are needed for this failure.

Validation

• git diff --check
• ruff format --check utils/_context/_scenarios/__init__.py
• ruff check utils/_context/_scenarios/__init__.py
• python3 -m py_compile utils/_context/_scenarios/__init__.py

[github-actions]

CODEOWNERS have been resolved as:

utils/_context/_scenarios/__init__.py                                   @DataDog/system-tests-core

[datadog-datadog-prod-us1-2]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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