Document OpenTelemetry HTTP server convention

Closes gh-35358

Author: bclozel

framework-docs/modules/ROOT/pages/integration/observability.adoc

@@ -189,13 +189,13 @@ This observation uses the `io.micrometer.jakarta9.instrument.jms.DefaultJmsProce
 [[observability.http-server]]
 == HTTP Server instrumentation
 
-HTTP server exchange observations are created with the name `"http.server.requests"` for Servlet and Reactive applications.
+HTTP server exchange observations are created with the name `"http.server.requests"` for Servlet and Reactive applications,
+or "http.server.request.duration" if using the OpenTelemetry convention.
 
 [[observability.http-server.servlet]]
 === Servlet applications
 
 Applications need to configure the `org.springframework.web.filter.ServerHttpObservationFilter` Servlet filter in their application.
-It uses the `org.springframework.http.server.observation.DefaultServerRequestObservationConvention` by default, backed by the `ServerRequestObservationContext`.
 
 This will only record an observation as an error if the `Exception` has not been handled by the web framework and has bubbled up to the Servlet filter.
 Typically, all exceptions handled by Spring MVC's `@ExceptionHandler` and xref:web/webmvc/mvc-ann-rest-exceptions.adoc[`ProblemDetail` support] will not be recorded with the observation.
@@ -207,6 +207,11 @@ NOTE: Because the instrumentation is done at the Servlet Filter level, the obser
 Typically, Servlet container error handling is performed at a lower level and won't have any active observation or span.
 For this use case, a container-specific implementation is required, such as a `org.apache.catalina.Valve` for Tomcat; this is outside the scope of this project.
 
+[[observability.http-server.servlet.default]]
+==== Default Semantic Convention
+
+It uses the `org.springframework.http.server.observation.DefaultServerRequestObservationConvention` by default, backed by the `ServerRequestObservationContext`.
+
 By default, the following `KeyValues` are created:
 
 .Low cardinality Keys
@@ -228,6 +233,16 @@ By default, the following `KeyValues` are created:
 |`http.url` _(required)_|HTTP request URI.
 |===
 
+
+[[observability.http-server.servlet.otel]]
+==== OpenTelemetry Semantic Convention
+
+An OpenTelemetry variant is available with `org.springframework.http.server.observation.OpenTelemetryServerRequestObservationConvention`, backed by the `ServerRequestObservationContext`.
+
+This variant complies with the https://github.com/open-telemetry/semantic-conventions/blob/v1.36.0/docs/http/http-metrics.md[OpenTelemetry Semantic Conventions for HTTP Metrics (v1.36.0)]
+and the https://github.com/open-telemetry/semantic-conventions/blob/v1.36.0/docs/http/http-spans.md[OpenTelemetry Semantic Conventions for HTTP Spans (v1.36.0)].
+
+
 [[observability.http-server.reactive]]
 === Reactive applications