Refactor event logging functionality into broker

[hendrikmakait]

Closes #xxxx

• Tests added / passed
• Passes pre-commit run --all-files

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    29 files  ± 0      29 suites  ±0   11h 21m 31s ⏱️ +25s
 4 083 tests + 3   3 966 ✅ + 1    112 💤 ±0  5 ❌ +2 
55 230 runs  +42  52 789 ✅ +40  2 434 💤  - 1  7 ❌ +3 

For more details on these failures, see this check.

Results for commit 0422cf5. ± Comparison against base commit 147c505.

This pull request removes 2 and adds 5 tests. Note that renamed tests count towards both.

distributed.diagnostics.tests.test_scheduler_plugin ‑ test_log_event_plugin
distributed.diagnostics.tests.test_scheduler_plugin ‑ test_log_event_plugin_multiple_topics

distributed.tests.test_event_logging ‑ test_log_event_e2e
distributed.tests.test_event_logging ‑ test_log_event_plugin
distributed.tests.test_event_logging ‑ test_log_event_plugin_multiple_topics
distributed.tests.test_event_logging ‑ test_log_events
distributed.tests.test_event_logging ‑ test_topic_subscribe_unsubscribe

♻️ This comment has been updated with latest results.

[hendrikmakait]

I don't like hooking deeply into these private attributes but I don't care enough for now to do something about it.

[fjetter]

I'm not even sure if we need this event but let's postpone this decision

[hendrikmakait]

Note: Overall, our event logging mechanism is a weird mix of a push and a pull-based messaging architecture. We may want to revisit this, but generally, it works 🤷.