Switch to OpenTracing's ContextVarsScopeManager

[MadLittleMods]

Switch to OpenTracing's ContextVarsScopeManager instead of our own custom LogContextScopeManager.

This is now possible because the linked Twisted issue from this comment is resolved:

synapse/synapse/logging/scopecontextmanager.py

Lines 42 to 43 in 40edb10

	It would be nice just to use opentracing's ContextVarsScopeManager,
	but currently that doesn't work due to https://twistedmatrix.com/trac/ticket/10301.

This PR is spawning from exploring different possibilities to solve the scope loss problem I was encountering in #18804 (comment). This appears to solve the problem and I've added the additional test from there to this PR ✅

---

Related to #10342 (previously matrix-org/synapse#10342) where we also want to change our LoggingContext machinery to base ContextVar based.

Testing strategy

1. Run a Jaeger instance (https://www.jaegertracing.io/docs/1.6/getting-started/)

   $ docker run -d --name jaeger \
     -e COLLECTOR_ZIPKIN_HTTP_PORT=9411 \
     -p 5775:5775/udp \
     -p 6831:6831/udp \
     -p 6832:6832/udp \
     -p 5778:5778 \
     -p 16686:16686 \
     -p 14268:14268 \
     -p 9411:9411 \
     jaegertracing/all-in-one:1.59.0

2. Configure Synapse to use tracing:
   homeserver.yaml

   ## Tracing ##
   opentracing:
    enabled: true
    jaeger_config:
      sampler:
        type: const
        param: 1
      logging:
        false

3. Make sure the optional opentracing depdency is installed: poetry install --extras all
4. Run Synapse: poetry run synapse_homeserver --config-path homeserver.yaml
5. Make some requests: GET http://localhost:8008/_matrix/client/versions
6. Visit http://localhost:16686/search to view the traces
   • Select the correct service
   • Select a relevant 'Operation' like one of the Servlet's
   • Press 'Find Traces' button

I tested a few endpoints and the traces seem to look normal.

Dev notes

SYNAPSE_TEST_LOG_LEVEL=INFO poetry run trial tests.logging.test_opentracing

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Code style is correct (run the linters)

[MadLittleMods]

Even though we've removed the LogContextScopeManager now, I've decided to keep these tests around. They appear like good sanity checks to make sure our tracing still works with Twisted regardless of what we try to use.

[anoadragon453]

🚀

[MadLittleMods]

Thanks for the review @anoadragon453 🐍