[ffe] add dd agent resiliency test

[leoromanovsky]

Motivation

FFE (feature flag & experimentation) SDKs include a local configuration cache that allows flag evaluations to continue even when the APM agent becomes unavailable.

If the local cache fails to work while RC is down, then evaluations fall-back to programmatic defaults which is undesirable.

Changes

• Adds ability to container class to start/stop
• New test which starts the flagging SDK in a healthy state, shuts down the agent, pushes a new RC configuration (which can't be delivered) and tests whether the flagging SDK continues serving last good configuration.

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• If PR title starts with [<language>], double-check that only <language> is impacted by the change
• No system-tests internal is modified. Otherwise, I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added (or removed)?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

manifests/cpp.yml                                                       @DataDog/dd-trace-cpp
manifests/cpp_httpd.yml                                                 @DataDog/system-tests-core
manifests/cpp_nginx.yml                                                 @DataDog/system-tests-core
manifests/dotnet.yml                                                    @DataDog/apm-dotnet @DataDog/asm-dotnet
manifests/golang.yml                                                    @DataDog/dd-trace-go-guild
manifests/java.yml                                                      @DataDog/asm-java @DataDog/apm-java
manifests/nodejs.yml                                                    @DataDog/dd-trace-js
manifests/php.yml                                                       @DataDog/apm-php @DataDog/asm-php
manifests/python.yml                                                    @DataDog/apm-python @DataDog/asm-python
manifests/ruby.yml                                                      @DataDog/ruby-guild @DataDog/asm-ruby
manifests/rust.yml                                                      @DataDog/apm-rust
tests/test_feature_flag_exposures.py                                    @DataDog/system-tests-core
utils/_context/_scenarios/endtoend.py                                   @DataDog/system-tests-core
utils/_context/containers.py                                            @DataDog/system-tests-core