fix: add api_version breadcrumb to client docs

Author: noahdietz

gapic-generator-java/src/main/java/com/google/api/generator/gapic/composer/comment/ServiceClientCommentComposer.java

@@ -108,9 +108,18 @@ public static List<CommentStatement> createClassHeaderComments(
       String secondaryTransport) {
     JavaDocComment.Builder classHeaderJavadocBuilder = JavaDocComment.builder();
     if (service.hasDescription()) {
+      String description = service.description();
+
+      // Include google.api.api_version breadcrumb comment.
+      if (service.hasApiVersion()) {
+        description =
+            String.format(
+                "%s\n\nThis client uses %s version %s.",
+                description, service.apiShortName(), service.apiVersion());
+      }
+
       String descriptionComment =
-          CommentFormatter.formatAsJavaDocComment(
-              service.description(), SERVICE_DESCRIPTION_SUMMARY_PATTERN);
+          CommentFormatter.formatAsJavaDocComment(description, SERVICE_DESCRIPTION_SUMMARY_PATTERN);
       classHeaderJavadocBuilder = classHeaderJavadocBuilder.addUnescapedComment(descriptionComment);
     }
 

gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpc/goldens/EchoClient.golden

@@ -35,6 +35,8 @@ import javax.annotation.Generated;
  * methods that explicitly implement server delay, and paginated calls. Set the 'showcase-trailer'
  * metadata key on any method to have the values echoed in the response trailers.
  *
+ * This client uses Echo version v1_20240408.
+ *
  * <p>This class provides the ability to make remote calls to the backing service through method
  * calls that map to API methods. Sample code to get started:
  *

java-showcase/gapic-showcase/src/main/java/com/google/showcase/v1beta1/EchoClient.java

@@ -59,6 +59,8 @@
  * 'x-goog-request-params' metadata key on any method to have the values echoed in the response
  * headers.
  *
+ * This client uses Echo version v1_20240408.
+ *
  * <p>This class provides the ability to make remote calls to the backing service through method
  * calls that map to API methods. Sample code to get started:
  *