fix: Switch instrumentation code to return version stored in DEFAULT_INSTRUMENTATION_VERSION (#918)

* feat: Add support for instrumentation version annotations

* fix: Switch instrumentation code to return version stored in DEFAULT_INSTRUMENTATION_VERSION

* Add comment for release-please versions

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: losalex

src/main/java/com/google/cloud/logging/logback/LoggingAppender.java

@@ -104,7 +104,10 @@ public class LoggingAppender extends UnsynchronizedAppenderBase<ILoggingEvent> {
   private static final List<LoggingEventEnhancer> DEFAULT_LOGGING_EVENT_ENHANCERS =
       ImmutableList.<LoggingEventEnhancer>of(new MDCEventEnhancer());
   public static final String JAVA_LOGBACK_LIBRARY_NAME = "java-logback";
-  // {x-version-update:google-cloud-logging-logback:current}
+  // Using release-please annotations to update DEFAULT_INSTRUMENTATION_VERSION with latest version.
+  // See
+  // https://github.com/googleapis/release-please/blob/main/docs/customizing.md#updating-arbitrary-files
+  // {x-version-update-start:google-cloud-logging-logback:current}
   public static final String DEFAULT_INSTRUMENTATION_VERSION = "1.0.0";
   // {x-version-update-end}
   private static boolean instrumentationAdded = false;
@@ -348,7 +351,7 @@ protected void append(ILoggingEvent e) {
     if (!setInstrumentationStatus(true)) {
       entriesList.add(
           Instrumentation.createDiagnosticEntry(
-              JAVA_LOGBACK_LIBRARY_NAME, Instrumentation.getLibraryVersion(LoggingAppender.class)));
+              JAVA_LOGBACK_LIBRARY_NAME, DEFAULT_INSTRUMENTATION_VERSION));
     }
     Iterable<LogEntry> entries = entriesList;
     if (autoPopulateMetadata) {