Check plugin registration status

[jayavenkatesh19]

Closes #9106

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

Adds a client side function to check if a plugin is registered on either the scheduler, worker or nanny registries. The plugin names seem to be unique enough to ignore the edge case where two different plugin types such as a WorkerPlugin and a SchedulerPlugin have the same name. The scheduler has separate functions added for this use case but will need to add extra client functions to separate the has_plugin function into has_worker_plugin etc.

Apart from checking if a plugin is registered by passing its name, also added the functionality of passing the plugin object itself with name extraction handled by the function. This is especially useful while using built-in plugins for users who do not know about the plugin.name attribute. Also added an error check for plugins whose name is not set.

CC: @jacobtomlinson

[github-actions[bot]]

Unit Test Results

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

    27 files  ±  0      27 suites  ±0   9h 53m 26s ⏱️ + 16m 50s  4 126 tests + 15   4 018 ✅ + 16    104 💤 ±0  4 ❌ ±0  51 698 runs  +194  49 510 ✅ +195  2 184 💤 ±0  4 ❌ ±0 

For more details on these failures, see this check.

Results for commit e5cf6331. ± Comparison against base commit 8e604a01.

:recycle: This comment has been updated with latest results.