Update file watcher to detect file write event (open-telemetry#2334)

* adding file write event

* adding issue link

.chloggen/target-allocator-file-watch.yaml

@@ -0,0 +1,16 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. operator, target allocator, github action)
+component: target allocator
+
+# A brief description of the change. Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Update file watcher to detect file write events
+
+# One or more tracking issues related to the change
+issues: [2349]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

cmd/otel-allocator/watcher/file.go

@@ -70,7 +70,9 @@ func (f *FileWatcher) Watch(upstreamEvents chan Event, upstreamErrors chan error
 		case <-f.closer:
 			return nil
 		case fileEvent := <-f.watcher.Events:
-			if fileEvent.Op == fsnotify.Create {
+			// Using Op.Has as per this doc - https://github.com/fsnotify/fsnotify/blob/9342b6df577910c6eac718dc62845d8c95f8548b/fsnotify.go#L30
+			if fileEvent.Op.Has(fsnotify.Create) || fileEvent.Op.Has(fsnotify.Write) {
+				f.logger.Info("File change detected", "event", fileEvent.Op.String())
 				upstreamEvents <- Event{
 					Source:  EventSourceConfigMap,
 					Watcher: Watcher(f),