Introduce StashNotifierDefault annotation

Simplifies HttpNotifierSelector implementations by allowing authors to
easily inject the plugin's default to fall back to.

src/main/java/org/jenkinsci/plugins/stashNotifier/StashNotifierDefault.java

@@ -0,0 +1,20 @@
+package org.jenkinsci.plugins.stashNotifier;
+
+import javax.inject.Qualifier;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+/**
+ * Use this annotation to inject the default value of
+ * {@link HttpNotifierSelector} or {@link HttpNotifier}.
+ */
+@Qualifier
+@Target({ FIELD, PARAMETER, METHOD })
+@Retention(RUNTIME)
+public @interface StashNotifierDefault {
+}

src/main/java/org/jenkinsci/plugins/stashNotifier/StashNotifierModule.java

@@ -21,9 +21,16 @@ protected void configure() {
 
     @Provides
     @Singleton
-    @Named("fallback")
-    HttpNotifierSelector providesDefaultApacheHttpNotifierSelector() {
-        return new DefaultHttpNotifierSelector(new DefaultApacheHttpNotifier());
+    @StashNotifierDefault
+    HttpNotifier providesDefaultHttpNotifier() {
+        return new DefaultApacheHttpNotifier();
+    }
+
+    @Provides
+    @Singleton
+    @StashNotifierDefault
+    HttpNotifierSelector providesDefaultApacheHttpNotifierSelector(@StashNotifierDefault HttpNotifier httpNotifier) {
+        return new DefaultHttpNotifierSelector(httpNotifier);
     }
 
     @Provides
@@ -33,7 +40,7 @@ List<HttpNotifierSelector> providesHttpNotifierSelectors() {
 
     @Provides
     @Singleton
-    HttpNotifierSelector providesHttpNotifierSelector(@Named("fallback") HttpNotifierSelector fallback,
+    HttpNotifierSelector providesHttpNotifierSelector(@StashNotifierDefault HttpNotifierSelector fallback,
                                                       @Named("preferredHttpNotifierSelector") String preferredHttpNotifierSelector,
                                                       List<HttpNotifierSelector> httpNotifierSelectors) {
         HttpNotifierSelector selector = httpNotifierSelectors.stream()