ObservableScheduledExecutorService not shut down gracefully enough

[llehtinen]

ObservableScheduledExecutorService from tw-observability-base gets shut down like any other executor service 1️⃣, which can cause noisy errors during shutdown: https://rollbar.com/Wise/fin/items/19353/ (relevant logs):

java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask@1398b0cd[Not completed, task = java.util.concurrent.Executors$RunnableAdapter@1d07069f[Wrapped task = io.micrometer.core.instrument.Timer$$Lambda$2367/0x0000000801f77ae0@228d9ce7]] rejected from java.util.concurrent.ScheduledThreadPoolExecutor@3d42f7d2[Shutting down, pool size = 10, active threads = 2, queued tasks = 6, completed tasks = 764]
	at java.base/java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2065)
	at java.base/java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:833)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor.delayedExecute(ScheduledThreadPoolExecutor.java:340)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor.schedule(ScheduledThreadPoolExecutor.java:562)
	at io.micrometer.core.instrument.internal.TimedScheduledExecutorService.schedule(TimedScheduledExecutorService.java:128)
	at com.transferwise.observability.base.internal.async.executor.ObservableScheduledExecutorService.schedule(ObservableScheduledExecutorService.java:20)

Ideally, the shutdown logic would find the delegate 2️⃣ in the screenshot, and apply the shutdownScheduledThreadPoolExecutor logic 3️⃣ to it:

    scheduledThreadPoolExecutor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
    scheduledThreadPoolExecutor.setContinueExistingPeriodicTasksAfterShutdownPolicy(false);
    scheduledThreadPoolExecutor.getQueue().clear();
    scheduledThreadPoolExecutor.shutdown();