Implement support for no recordings indicator on timeline (#18363)

* Indicate no recordings on the history timeline with gray hash marks

This commit includes a new backend API endpoint and the frontend changes needed to support this functionality

* don't show slashes for now

web/src/components/timeline/MotionSegment.tsx

@@ -15,6 +15,7 @@ type MotionSegmentProps = {
   timestampSpread: number;
   firstHalfMotionValue: number;
   secondHalfMotionValue: number;
+  hasRecording?: boolean;
   motionOnly: boolean;
   showMinimap: boolean;
   minimapStartTime?: number;
@@ -31,6 +32,7 @@ export function MotionSegment({
   timestampSpread,
   firstHalfMotionValue,
   secondHalfMotionValue,
+  hasRecording,
   motionOnly,
   showMinimap,
   minimapStartTime,
@@ -176,6 +178,12 @@ export function MotionSegment({
             segmentClasses,
             severity[0] && "bg-gradient-to-r",
             severity[0] && severityColorsBg[severity[0]],
+            // TODO: will update this for 0.17
+            false &&
+              hasRecording == false &&
+              firstHalfMotionValue == 0 &&
+              secondHalfMotionValue == 0 &&
+              "bg-slashes",
           )}
           onClick={segmentClick}
           onTouchEnd={(event) => handleTouchStart(event, segmentClick)}