Bug 1425173 - Fix the missing "search" category and extend the expire time for FX_PREFERENCES_CATEGORY_OPENED_V2 r=jaws

- Extend the expire time from 59 to 66

- While going to one pane we will send the "FX_PREFERENCES_CATEGORY_OPENED_V2" telemetry for that pane. However, the "search" pane category was forgotten to be put in the Histograms.json like other pane categories. As a result, we saw "Unknown label for categorical histogram" logged in the browser console when opening about:preferences#search

MozReview-Commit-ID: HJZrAlCncKA

--HG--
extra : rebase_source : 6eb7e0b82090ae33787f4d85cf9a12c9500f2492

toolkit/components/telemetry/Histograms.json

@@ -6548,11 +6548,11 @@
   },
   "FX_PREFERENCES_CATEGORY_OPENED_V2": {
     "record_in_processes": ["main", "content"],
-    "bug_numbers": [1335907],
+    "bug_numbers": [1335907, 1425173],
     "alert_emails": ["jaws@mozilla.com"],
-    "expires_in_version": "59",
+    "expires_in_version": "66",
     "kind": "categorical",
-    "labels": ["unknown", "searchresults", "general", "applications", "privacy", "sync", "advanced"],
+    "labels": ["unknown", "searchresults", "general", "applications", "privacy", "sync", "advanced", "search"],
     "releaseChannelCollection": "opt-out",
     "description": "Count how often each preference category is opened."
   },