SpringBoot Move MVC metrics auto-configuration to the new Observation instrumentation

Since spring-projects/spring-framework#28880, Spring Framework now instruments directly Spring MVC with the HttpRequestsObservationFilter, removing the need for a custom WebMvcMetricsFilter.

With this issue, we should update the auto-configuration to only rely on the new ObservationRegistry and configure the instrumentation available on Spring MVC. We need to provide a smooth upgrade experience: deprecate the tags providers and adapt them to the new infrastructure until it's completely removed.