Inject ObjectProvider into BeanPostProcessors to avoid premature initialization of OpenTelemetry

[HaloFour]

When a BeanPostProcessor takes a dependency on a bean directly it forces that bean and it's dependencies to be immediately instantiated. This can create a situation where those dependencies might not be post-processed by other BeanPostProcessors that have not yet been initialized. By injecting ObjectProvider<T> into the BeanPostProcessors the initialization of those dependencies can be deferred avoiding this issue.

[HaloFour]

I had been bitten by this as I have a custom SpanExporter implementation that uses MeterRegistry to report span metrics to prometheus. These BeanPostProcessors were causing OpenTelemetry and my SpanExporter to be instantiated which was causing MeterRegistry to also be initialized before MeterRegistryPostProcessor was available. That was causing my MeterRegistryCustomizer to not be processed resulting in custom tags not being applied to any metrics.

I've not found any written documentation that states that BeanPostProcessors should always use ObjectProvider<T> or @Lazy but it seems like the safest route to take.