feat: add notifications table and Electric SQL replication setup

- Introduced a new notifications table with relevant fields and indexes.
- Configured Electric SQL replication for the notifications, search_source_connectors, and documents tables.
- Centralized Electric SQL user credentials in the migration script for better management.
- Ensured idempotency in the migration process for creating users and publications.

surfsense_web/app/dashboard/[search_space_id]/documents/(manage)/components/DocumentsTableShell.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { ChevronDown, ChevronUp, FileX, Plus } from "lucide-react";
+import { ChevronDown, ChevronUp, FileX, Loader2, Plus } from "lucide-react";
 import { motion } from "motion/react";
 import { useParams } from "next/navigation";
 import { useTranslations } from "next-intl";
@@ -114,7 +114,7 @@ export function DocumentsTableShell({
 			{loading ? (
 				<div className="flex h-[400px] w-full items-center justify-center">
 					<div className="flex flex-col items-center gap-2">
-						<div className="h-8 w-8 animate-spin rounded-full border-b-2 border-primary"></div>
+						<Loader2 className="h-8 w-8 animate-spin text-primary" />
 						<p className="text-sm text-muted-foreground">{t("loading")}</p>
 					</div>
 				</div>