feat: Add support for instrumentation version annotations (#916)

Author: losalex

.github/release-please.yml

@@ -6,3 +6,5 @@ branches:
     handleGHRelease: true
     releaseType: java-yoshi
     branch: java7
+extraFiles:
+  - src/main/java/com/google/cloud/logging/logback/LoggingAppender.java

owlbot.py

@@ -24,6 +24,7 @@
     '.github/blunderbuss.yml',
     'CONTRIBUTING.md',
     '.github/auto-label.yaml',
+    ".github/release-please.yml",
 ])
 
 # --------------------------------------------------------------------------

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

@@ -104,6 +104,9 @@ 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}
+  public static final String DEFAULT_INSTRUMENTATION_VERSION = "1.0.0";
+  // {x-version-update-end}
   private static boolean instrumentationAdded = false;
   private static Object instrumentationLock = new Object();