Adding correctness in the ReplyCount generation (#14047)

* Adding correctness in the ReplyCount generation

* Applying suggestion from reflog

* More reliable reply count generation

* Some tests fixed

* Adding i18n translation

* Fixing reply count on save behavior

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

i18n/en.json

@@ -6618,6 +6618,10 @@
     "id": "store.sql_post.permanent_delete_by_user.too_many.app_error",
     "translation": "Unable to select the posts to delete for the user (too many), please re-run."
   },
+  {
+    "id": "store.sql_post.populate_reply_count.app_error",
+    "translation": "Unable to get the post replies count"
+  },
   {
     "id": "store.sql_post.save.app_error",
     "translation": "Unable to save the Post."