[CCA WebUI] Extend flag "camera-system-web-app" in flag-metadata.json

Extend it to milestone 89.

Bug: 980846
Test: None
Change-Id: I599339e61a5578ce25edeedffff2bbb86d76d7f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450138
Auto-Submit: Wei Lee <wtlee@chromium.org>
Reviewed-by: Shik Chen <shik@chromium.org>
Commit-Queue: Wei Lee <wtlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814103}

chrome/browser/flag-metadata.json

@@ -454,7 +454,7 @@
   {
     "name": "camera-system-web-app",
     "owners": [ "chromeos-camera-eng@google.com" ],
-    "expiry_milestone": 87
+    "expiry_milestone": 89
   },
   {
     "name": "cast-media-route-provider",