Update link to the official Micrometer @Timed documentation

[gheyle]

The current link of the official Micrometer @timed annotation documentation is at: https://docs.micrometer.io/micrometer/reference/concepts/timers.html#_the_timed_annotation, while the current Spring Boot documentation at

spring-boot/spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/actuator/metrics.adoc

Line 1129 in b82830c

Please refer to the {url-micrometer-docs-concepts}#_the_timed_annotation[Micrometer documentation].

points to https://docs.micrometer.io/micrometer/reference/concepts#_the_timed_annotation.

[snicoll]

Thanks for the report.

Closing in favor of PR #42467