fix(classifier): set started_at timestamp when annotation starts

- add `metadata._inProgress` to classifications, and set it to true when a volunteer first updates an annotation.
- set `classification.metadata.started_at` to the current time when `metadata._inProgress` is set to true.

app/classifier/classifier.jsx

@@ -141,9 +141,15 @@ class Classifier extends React.Component {
       });
   }
 
-  updateAnnotations(annotations) {
+  updateAnnotations(annotations, fromUserAction = false) {
     this.setState({ annotations });
     this.props.actions.classify.saveAnnotations(annotations);
+    if (fromUserAction && !this.props.classification?.metadata._inProgress) {
+      this.props.actions.classify.updateMetadata({ 
+        _inProgress: true,
+        started_at: new Date().toISOString()
+       });
+    }
   }
 
   updateFeedback(taskId) {
@@ -203,12 +209,13 @@ class Classifier extends React.Component {
     actions.classify.updateMetadata({ subject_dimensions });
   }
 
+  // handle annotation changes from the subject viewer eg. drawing tasks
   handleAnnotationChange(classification, newAnnotation) {
     const { annotations } = this.state;
     const index = findLastIndex(annotations, annotation => annotation.task === newAnnotation.task);
     if (index > -1) {
       annotations[index] = newAnnotation;
-      this.updateAnnotations(annotations);
+      this.updateAnnotations(annotations, true);
     }
   }
 

app/classifier/task.jsx

@@ -16,7 +16,7 @@ class Task extends React.Component {
     const index = findLastIndex(annotations, annotation => annotation.task === newAnnotation.task);
     if (index > -1) {
       annotations[index] = newAnnotation;
-      this.props.updateAnnotations(annotations);
+      this.props.updateAnnotations(annotations, true);
     }
   }
 

app/redux/ducks/classify.js

@@ -51,6 +51,7 @@ function createNewClassification(project, workflow, subject, goldStandardMode, l
   // Delete the metadata key because we don't want volunteers to see it.
   subject.update({ 'metadata.intervention': undefined });
   const newMetadata = {
+    _inProgress: false,
     workflow_version: workflow.version,
     started_at: (new Date()).toISOString(),
     user_agent: navigator.userAgent,