Prior to this commit, the Micrometer instrumentation support would
auto-configure a `ServerHttpObservationFilter` for creating observations
in Spring MVC applications.
As of Spring Framework 6.2, applications can extend this filter class to
get notified of the observation scope being opened.
This commit contributes a new `TraceHeaderObservationFilter`
implementation that writes the current Trace Id (if present) to the
`X-Trace-Id` HTTP response header.
This feature is disabled by default, applications will need to enable
`management.observations.http.server.requests.write-trace-header`.
`
Closes gh-40857
afcc780e61