Micrometer tracing auto-configuration doesn't register all ObservationHandlers

[mhalbritter]

It seems that the micrometer tracing auto-configuration doesn't register all ObservationHandlers at the ObservationRegistry.

ObservationRegistryPostProcessor runs, calls ObservationRegistryConfigurer#configure, which uses an ObjectProvider<ObservationHandler<Context>> to get all ObservationHandlers. This call only returns the bean from MicrometerTracingAutoConfiguration#defaultTracingObservationHandler, and not the ones from MicrometerTracingAutoConfiguration#httpServerTracingObservationHandler or MicrometerTracingAutoConfiguration#httpClientTracingObservationHandler.

[mhalbritter]

There's an ugly unchecked cast with a rawtype needed, this can be removed once Micrometer 1.10.0-M3 is released.